I've never heard that better expressed than here:
"When you're discussing drilling in ANWR with a progressive, make no mistake — you are, more or less, having a debate on whether or not you should be allowed to strike him in the face." – Ace of Spades
So many of them have latched onto these causes as a key to their persona, as a way to self-define, that to attack their politics is interpreted as a personal insult. "I disagree with your politics" translates to "I disagree with the CORE OF YOUR VERY IDENTITY, you stupid asshole."
The Right must be careful not to fall into the same trap; the possibility has occurred to me that we are not immune.