What do you belive in?

Are we ever "free" to choose our religion?
I feel ashamed for those who try to push people into believing the same things they do.
I was surprised when two Mormons came to talk to my brother about his beliefs. My brother is a very opinionated man and he is atheist and believes that there could be a God yet however he doesn't feel like we should pray to him in order to get what we want instead he believes we should work for it. So the Mormon guys knock on the door for a friendly talk, and I was glad because I like hearing different points of views, but however once they got to talk to him they insulted his beliefs saying he had to believe in what they believed because they were right. My brother laughed at how ridiculous it was, and they said he was possessed by the devil.
I find that absolutely disrespectful. Just because he doesn't believe in God it shouldn't mean he has to believe in the devil.
A few weeks later they sent him a book asking him to read it and it would help him realize he was wrong.
How wrong is that?
I understand they want to spread the word but insulting is not the way, aren't we supposed to treat others like we want to be treated?
If their beliefs in God are so strong then why would they do such thing?
I don't have the same beliefs, I believe in God, and Jesus Christ, I pray as much as I can, but if someone tried to change my opinion I would feel insulted as well.

And what brings me to writing this is that aren't we supposed to be free to choose our religion yet we have people pushing us to believe otherwise? Can't we spread the word without humiliating or insulting others? Or can't we just respect their choice?