I don't think there's such a thing as a 'bad' genre. Each to their own. I certainly wouldn't think any less of someone for their reading choice, and I'd like to think people would extend the same courtesy to me.
Given that the main purpose of fiction is to entertain, followed rather distantly by the purpose of teaching readers about the world, I can't condemn any particular genre. I read widely. Horror, mainstream, experimental literary fic, science fiction, fantasy, historical fiction, thrillers, young adult in several flavors of genre, apocalyptic. I haven't read much bizarro, or much romance, although goodness knows there are bizarro-esque and romantic tinges in some of the other genres I've read. I honestly don't get why people do condemn certain genres. I mean, it's one thing to say that you yourself don't enjoy reading a particular genre. It's quite another to say that science fiction is all crap, or that Westerns are predictable dreck, or that the only romance book that didn't suck was written by Jane Austen a century ago. It's a blanket condemnation, a "well this is what I think and my opinion is clearly more important than the millions of science fiction readers out there." I mean, if you're okay with knowing you've shown your ego to be the size of some planets, that's fine. Just know that your listener will understand that to mean, "The speaker is unable to look at this issue with any perspective. I wonder what else they've distorted in the telling."
Totally agree with the words above. One book I read and loved was What Dreams May Come by Richard Matheson, and whenever I think of the book now all I think is "beautiful love story." Whatever else the book is, to me it is a love story. I have read five or six Mills & Boon books (on a dare!) and they were absolutely appalling. The same friend also dared me to write and submit a book to Mills & Boon, and I actually started writing it, but I had to stop pretty quickly because I just liked my characters too much to put them through the contrived, sad rubbish that is a Mills & Boon story. These are not love stories. They are mulch for the garden There may very well be a couple of stand-outs among the fifty gazillion books they publish every year, but I'm not willing to troll through them all to find out. So if I had to say I look down on any particular books, these would be the ones. Apart from that, I'll read anything if it's written well, whether it be horror, humor, sci-fi, fantasy, historical, travel, romance, whatever.