The kind of individual who shoots someone for saying things he doesn't like is a narcissist.
Ideas anger narcissists because if they are counter to what they already believe, they are a personal affront, and if they cannot reason the challenge away because - quite simply, they're wrong and the other person is right - it creates a great anger in them.
And narcissism is prevailing in our culture currently. People far prefer to call the other side bad, stupid, etc, rather than introspect and consider that maybe you're not that smart, and maybe you don't know everything, and maybe what you believe is actually naive and just a manifestation of your sillyness.
The problem of course is that the only way opposing narcissists can overcome each other is by force. So there'll be less argument, and more go-straight-to violence.