Why do so many people have rotten attitudes?

I am a nice person, I believe in seeing the good in all people, but it seems like no matter where I go or who ever I talk to they just make insults, curse at people, make fun of people, etc. I rarely find nice people who want to have intelligent non-insulting conversations rather they find someone walking down the street and say insulting things or start going off about some random person insulting their behavior or something. It seems like everyone has a rotten or negative attitude about something. I normally just sit there and don't say anything just because I don't want to start a fight by telling them I think they are being rude, and because I don't really agree with them. The people I do know who are nice are normally homebodies or have families they spend most of their time with etc.