I'm really getting annoyed with these people...help?

I like to stand up for people that get made fun of. I don't think bullying's ok. I'm 13 and people treat me like I'm the most worthless, pointless thing ever and it really hurts. For example, today I saw all these comments on a video. All they were about was how slutty the other person was and it's just because one person liked the song and the person who didnt thought they were stupid cuz the other liked it. I see these comments all the time. People are hurtful and ignorent. Half of us don't care about another person's feelings and I just find it sick. I honestly don't care about myself but that doesn't mean I have to be insensitive to the people who do have respect for themselves and stuff right? Why can't people who are older then me see that? Anyway so I wrote a comment to no one in particular saying we should all just accept that people like different things and that those who don't understand that need to try not to be so selfish. I got like fifty thumbs up and tons of ppl were thanking me, but there was this one guy who said something really gross to me that was really immature and plain mean. I went to his profile so I could block him then saw all the other stuff he's got there. people are commenting about how much they hate him, and he even has a list on the info thing of usernames he hates. And u can see how rude he is on the thing where it says other comments he's made on different vids. Anyway, I don't understand these people. I can't live with people like this.. I'd rather just jump off a cliff and I'm rlly not kidding. What goes on in their minds? Why are they doing this? And how can I keep ensuring the happiness of others without feeling hurt by them? Thanks so much :) oh and I think the usernames like TheShredder203 but there's tons of them out there that still do that... He's got this thing against emo's and all that. I'm not near being one, but I know two people who are and they are like the most amazing people in my life. They're the reason I haven't given up so it kinda upsets me when ppl have issues with others that might be like my friends. Please help! It's really upsetting me. Oh and if ur gonna make me feel worse, please don't write anything.