It has nothing to do with Schilling as a person. He didn't respond, he identified the losers and a couple paid for their stupidity. Everyone has a right to free speech, but that doesn't mean there aren't consequences for what they say.
So the guy congratulated his daughter for getting a scholarship. Does that deserve rape threats against her?
It isn't just Twitter, it's forums like this too. People think hiding behind the keyboard gives them the right to say what they want. Knowing they would never speak to someone's face that way. Internet tough guys.