Depends on what you mean by online. Online the internet? Online PMC?
Online the internet, that also depends what website you are on. If you are on a site with lots of people and really bad moderation you're bond to run into tons of trolls. People want attention and they will do anything to get it. Oh and some people just like causing misery for others.
There are a lot of people who aren't trolls online, you just have to find them.