I was told off once for calling right-wing extremists pigs, along the lines of "Do you think callling people pigs will change their minds?" - I had to explain (with some exasperation, I might add) that if someone earns the "pig" label they're beyond changing & I'm not addressing them at all; I'm letting everyone else know that if the thought "Those people are pigs" occurs to them, they're neither wrong nor alone.
Also, this Patton Oswalt bit: https://www.youtube.com/watch?v=AkKo1_RP_0c