>>/44071/
> But these guys, these shooters, aren't force people to do anything, just go out and try to kill people 

Terrorist is just a term like "bad guy" now. Classic wars in Post-WW2 world are forbidden "on paper", so most of conflicts in last 50 years are so-called military operations, where word "terrorist" became synonym of enemy combatant. It is easy to label everyone now as terrorist, because common person would easily understand that. 

Or "freedom fighter" if it is good guy, but in case of domestic terrorism freedom is already achieved, so only terrorists are against it.