There's another angle to this. This is poking fun at how conservatives concede ground immediately in debates with leftists, giving them the leverage and the conservative thus having to work from the left's view of the world. In this case homophobia being bad. Normally a conservative would try to argue with a leftist that Christianity isn't homophobic. By engaging in that direction they've already conceded to the leftist that homophobia is bad, which means that they are now on the run and the leftist can continue chipping at them. It's a losing strategy for an argument.
Another example could be used for a race. There was a crappy meme I remember seeing a few years ago that illustrated this perfectly. If you admitted that the position you're taking is a racist one, a leftist would be shocked at the fact that you aren't arguing with them over it not being racist. The fact that they haven't shamed you into accepting racism is evil rots their mind.
Once you refuse to concede racism being bad, suddenly the leftist's argument goes from "Why isn't X racist?" to "Why aren't you arguing with me over why you think it's not racist?"
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Both Stonetoss's comic and the meme above are illustrating an important point for right-wingers: when you don't let the left shame you into accepting the foundation for the left's argument and their worldview as a whole, the left suddenly has no idea what to do. You shouldn't play by the rules that the left has set for the argument is a much simpler way to put it.