Good question. I think it has to do with empathy. When arguing on the internet, you dont have an actual person in mind that you are talking to. Also, anonymity gives you safety. You dont have to worry about not hurting someone because it wont have adverse effects on the relationships with people around you, aka your tribe. This was essential for survival some time ago and sits deep within our subconcious.
There are very few people in first world countries who cant feed themselves