It's pretty common for people to take a stance similar to the commenter linked above - that any critique of their ideas is like lumping them in with Republicans. (Which to them is the same as saying they're evil.)
They don't recognize that 1) on some scales they are closer to Republicans than the leftist they're talking to, that the political spectrum is much larger than they imagine and 2) their own positions also put the very lives of some groups at risk