Read the title.
I'll put in as a starting point:
As it is nearly impossible to know who is behind that name in purple over my head, you therefore have no idea who I really am.
As typing is easier to undo than saying, therefore I can put myself across as a totally different person to whom I really am.
This means that someone who you originally feel to be trustworthy may in fact be manipulating you for their own advantage.
It is much harder to notice if someone is manipulating you online as things such as 'body language' don't exist there.
Do you feel creeped out now? Here's a bit more.
The vast majority of people are selfish at heart, even if they manage to overrule it. This is due to essentially animal instinct, as genes are selfish.
People who are intelligent enough are able to disguise that.
People who are intelligent enough are even able to overrule selfishness, although it's generally easy to tell because actual kind people have a different body language.
OK, how secure do you feel now on the Internet?
I feel completely secure, as long as I don't download any identity-stealing viruses. I could care less who you are in real life. As I learned from Kirito of SAO (which everyone should go watch), who you are on the internet reflects who you are in real life. It might not be directly, but in some way it is true. Do I care if you're actually a 45-year-old sociopath, instead of the ten-year-old kid you're pretending to be? No. Why would I? You act a certain way on the internet, that is how I judge you. Let's say you decide to post a terrible suggestion in the suggestions forums with terrible detail and atrocious grammar, and then act hyperdefensive when anyone criticizes your idea and basically hate everyone for no reason. (no names.) Do I care if you're actually a college professor doing a social experiment, or a 20-year-old who decided trolling this group of try-hard no-lifers over the internet would be funny? No. I'm going to assume based on your actions that you're a spoiled, immature, impatient human being who is most likely a child.
P.S. Why do I feel that this is so much more important than my U.S. history homework that I felt the need to type it at 10P.M. instead of finishing the homework? 0.o