The big difference between calling someone a Jew meaning a swindle & a rip-off is that the word Jew can only be read one way, i.e. as a reference to Jewish people. Black face paint has more than one reading, some of which have been given throughout the post. Take the Witchmen for example, the black-face viewed in context of the costume, the name of the side & the actual form the entertainment takes is evidently not the same as a minstrel performance.

As to where the offence is grounded, I am with you to a point. However, speaking as a gay man myself, I despise the constant assumption by some people that I need protecting from all manner of phrases & behaviours as though I am not capable of rising above them or that I am somehow programmed to take offence at all sorts of things that quite frankly I couldn't care less about. Like any other person I am more than capable of speaking up for myself & don't need others to be offended on my behalf. When you're part of a minority group you develop a fairly thick skin & have little need to look for discrimination & parody where none is intended.