The thing I've found (having had several gay friends in the past, and knowing plenty more) is that so many homosexuals like to flaunt their sexuality- a lot of times it's very "in your face". I don't hate THEM for it; I dislike their lifestyle, I dislike their attitude towards straight people sometimes, sure, but I don't hate them.
Like Ugly said, they pretty much shoot themselves in the foot- one of my friends "came out of the closet" to me a long time ago, and he asked me if it bothered me that he was gay. I told him, "It does, because I don't think it's right, but I'm not upset with you over it", and he FLIPPED OUT on me. I was suddenly a homophobe, a hater, and a bunch of other things that hey OUCH, that's not a nice thing to call anyone.
And yet he still wanted my acceptance and approval? Er...
There are straight people who do the same sort of thing, though. I stopped hanging out with some friends who spent every night at the bar getting wasted; they called me uptight, Little Miss Perfect, all kinds of things. I would have been fine still talking with them sometimes, I just didn't want to do what they were doing anymore. I didn't even say anything to them, except "Nah, I don't really want to go to the bar anymore".
People who are in the midst of sinful behavior(s) want company. They want to be indulged. Not just "accepted" but encouraged, told that it's ok to do what they're doing.
So my answer to the OP is: Sometimes it is more difficult to remain friends/make friends with people indulging in certain behaviors than others. Some of my gay friends are easier to be around than others, some of my friends who drink don't make me feel like a jerk for not drinking with them anymore and I can be around them, and I'm sure some of my friends lie or whatever else, but what it comes down to is that I don't "unfriend" people JUST BECAUSE they sin, I stop being friends with people because they act like jerks.
...uh...yeah.