Would like to bring up the topic of when you have a main character or characters do bad things. That is, "unpopular things". If a character murders a serial rapist, your readers are more likely to cheer and sympathize/relate to them more. If, however, you have them murder a security guard who witnessed them committing a crime... then it becomes challenging keeping the character in a state where others care about them. There are two main ways to solve this problem which come to mind. A) Make them into a badguy or anti-hero--make the readers see the character as an enemy whom they want to see stopped. B) Have it as a character's fall on their path to damnation, possibly with redemption in mind for the end. Would like to present a particular scenario I have considered before. A situation where the main character does something the readers will consider bad, but within the setting it is seen as highly normal. For example, taking a fellow lord's children as hostages was a common practice to ensure treaties and deals would be kept, in many cultures. Were the treaty broken... the children would be killed--sometimes in a very unpleasant manner. The easy solution when faced with such a circumstance, is for the character to not harm the children despite the other lord breaking the pact. Discussing how to do things the easy way is rarely interesting. How would you go about having a character perform malpractices without portraying them as the badguy, and without having the story be their "fall from grace"?
Everyone does wrong things - what separates us from the nuts is that we know it's wrong, we feel shame, guilt, remorse. Sometimes we try to deny these feelings through justification - building up walls of anger or resentment but usually they crumble. Feelings like these - an emotional and spiritual battle would let the reader know that the character is not evil - he's just done the wrong thing and looking to redeem himself.
Or the character feels they have no other choice. In the example of killing the children, to choose not to do so would be considered weak by the others in power - allies and enemies alike. That could make things very dicey for the MC and the people depending on him for protection. Many MCs do things they find distasteful, criminal, or morally reprehensible - but they do it because it has to be done. Get that point across and I think it works without making the MC the 'bad guy'.
Your post made me think of the movie "Road To Perdition", starring Tom Hanks. Hanks plays a 1930s-era mob hitman, which is pretty darn distasteful to most of us, but he is the protagonist. His character comes across as a good guy, partly because another hit man kills his wife and one of his sons, so he's justified in taking revenge. He kills a few people and robs a few banks, but most of his victims deserve it, and besides, he's trying to protect his remaining son. I think it's a good example of a main character who does a lot of bad things, but still comes across to the audience as a hero of some sort. It's not really a "fall from grace" story or a "redemption" story. It's a hard man who does an ugly job trying to protect his son from falling into the same kind of life. Great movie - check it out.
As stated above, all character's do bad things. It's their reactions that separates them from being true 'bad guys.' I've got a character who committed genocide on an alien race after they gave her no choice-and it has haunted her for three years. So, yeah, characters do bad things all the time. The anti-hero won't care about much of what they do (think Richard B. Riddick from Pitch Black and the Chronicles of Riddick) and most villains won't care either. What separates good people from bad is conscience.
You can have the character do all kinds of bad things -- sometimes due to the environment they inhabit, sometimes due to some sort of psychological issue. But you can always give the character relatable by giving him some of the same fears and desires as the rest of us. Two huge examples of successful protagonists who do 'bad' things are Tony Soprano from The Sopranos and Dexter Morgan from Dexter. They're both murderers, and in Dexter's case, a serial killer. But we still like both of them and root for them. Because we see them dealing with other things that we deal with, but also because we see them at least somewhat conflicted by what they do, or at the very least, cognizant of the fact that they should be conflicted. Another interesting example of this, kind of in reverse, is the Walter White character from the television show Breaking Bad. Over the life of the series, we see him go from a very sympathetic character who starts manufacturing and selling meth due to some extreme circumstances, evolve into someone who we really do not like very much and becomes very immoral. The interesting thing here is how long it takes viewers to recognize that they're not really liking Walter so much anymore. Readers/viewers really want to like and root for the protagonist, and it doesn't take a whole lot to make him somewhat relatable (one common theme is that everyone wants to be loved -- that avenue there opens up all kinds of possibilities for what a protagonist might do, or want to do.) Once we do like him on some level, it takes longer than it seems like it should for us to turn against him.
I personally find it more irritating when a character does something stupid rather than bad. There are any number of justifications for doing "bad" things and very rarely are authors naive enough to simply attribute it to "they're just a bad guy". Those core motivations can make them a more interesting an engaging character. Stupid, on the other hand just makes a character... well, stupid. And I'm not talking "Hodor" stupid, I'm talking "steal the van to save the dog from zombies, despite the fact that zombies have literally no interest in it, putting everyone else's lives at risk" stupid.
Actually, I asked myself this for a YA idea I had the other day. It's borderline ultra-trashy, but I thought it would be fun to write. Then the further I got into it, the more I realised that it would definitely be more complex than I had originally intended. In it, my main character is some who is raised to revert to rage as his default response to everything, behave selfishly, and kill without hesitation or remorse. I had to figure out what about someone, who is essentially (forced into being) a serial killer, a reader would relate to. Sure, he's not all bad and he certainly places value on those he cares about, but objectively he is far worse than many of the people he kills in the name of justice. The first thing that redeems him is that he is well aware of his faults as a person. Although he doesn't have the capacity for self-loathing at the start of the story, you could be forgiven for thinking that it's his defining characteristic. He is charged hurting people as a matter of daily life, but he recognises just how much evil stains his own hands. Secondly, I decided that the best thing for the audience to relate to would be the wish for him to change. I decided that I had to write a character who does bad things, but has the capacity to grow into a good person. A good person can do bad things with the right(/wrong) intentions and not lose audience sympathy.
As long as it's in-keeping with the character. If MC was someone who loved puppies and lemonade and a warm day, then taking someone hostage for what ever reason seems like to far a turn into the dark side. But if they are inclined that way and you have built up a sympathetic side i cant see the issue.
The MC from one of my older stories once beat halfway to death his own apprentice just to prove a point (the point being: I can beat my apprentice half to death). In the end though he came across not quite hated by those that read it. If you can make your character seem evil and later redeem him or make it so that it turns out it was not really an evil act but an act of necessity in order to protect something it will be really interesting. (Plus if you can make your readers feel a little guilty for misjudging the main character then you get some ambivalent fans)
It's a matter of spin. Somebody's terrorist is someone else's freedom fighter. Sometimes it is possible to objectively separate the good guys from the bad, but often it isn't. As a writer, you need to convincingly present your character's point of view.
If the main character does something like this early on in the book, then I probably won't like it. However, if and when done later, it can be a dramatic way of saying 'who are the good guys, really?' and it can either question where you loyalties lie in the book, or sympathise with the character and try and work out why he's ding the things he's doing. When considering a series, such as George R. R. Martin's A song of Ice and Fire, then many of the 'main characters' do questionable things. There's nothing wrong with writing it, if you're comfortable in doing so. Hope I helped.
Hmm, that's a tricky one - I'm fond of 'bad' main characters, but I can see how it would be difficult to keep rooting for/caring about someone who would harm children. That said, I don't think it's impossible, and if you can pull it off it could be very powerful. I suppose you just need to be consistent with the personality of your MC, if its something that needs to be done but he's sickened by it then show that, even if it falls short of a full-on fall from grace. Perhaps there could be some 'punishment' that isn't dramatic but may prevent the MC seeming like a monster - he can no longer bond with his own kids, for example. it certainly sounds interesting, best of luck with it