I find that when someone respond to a post in an overly aggressive manner, they are not viewing or processing said post solely on what was written but are falvouring it with their own attitude. It's just text and unless read in as neutral a voice as possible, people will assume belligerence/rage/disdain/hyperbole/etc. because that's the mentality they are viewing it from, not whatever the poster wrote.
We all tend to have an initial gut reaction to a post that may get our hackles up. I find it best to read over any response I've types out before posting, re-read the post I'm responding to, then view both as neutral as possible. I may change wording or the entire thing, or just delete it altogether and move on.