I've only been part of one fandom in my life. I'm a brony. I wasn't at first. I was just having fun watching the show. But I slowly got sucked in to the point where I write stories about colorful cartoon horses and take pictures, something I thought I'd never, ever do. I did this because it was fun, and the part of the fandom that I stick with is always nice and encouraging to me. I have my own little group of followers and I talk with a few of the blog owners and everyone is very nice.
That being said, I have seen the ugly side of the fandom, usually in the comment sections of articles on EQD or on tumblr in some cases. And I keep wondering, "What's wrong with you? This is supposed to be fun. Relax!" And so, I have quickly learned to not read too far into the comment sections and just always tell people that I appreciate the art/story/craft/whatever it is they are doing, because I've found that that attitude makes me smile and be happy that I'm still part of the fandom.
On the flip side, I HAVE had a really bad experience with a fandom before. As others have pointed out, the Souls fandom was...not helpful, to say the least. I picked the game up because a friend of mine would not shut up about it. Gave it a shot, got stuck, asked him for help and he just laughed, saying, "Figure it out on your own." So I went to the internet--here even--and asked for help. And I was mocked. I remember one time I said I couldn't figure out how to get spells to work--turns out I was using a tailsman instead of a staff--and one person told me, "Shit. Did you never figure out how to attack either? It's basically the same thing, dumbass." So yeah, I quit the game because of people like that. No one was willing to help me. It wasn't until Dark Souls II came out, where the game explained things a bit better, that I went back and finally stomped Dark Souls into the ground.
So now, I make it a point to offer whatever help I can with any of those games, because I do think they're great and I don't want people to be chased away from them by losers like the ones I ran in to.