It's a sign of insecurity. Sometimes it's also a matter of things being misinterpreted during a tense argument and then an escalatory spiral. Text-based communication is easy to misconstrue, especially with people from so many different cultures.

I actually take the other side, though. Rapid escalation to name calling is the norm online. However, I've had many civil disagreements with people on Stacker News. Sometimes, one of us even changed their mind. How neat is that?