I think part of it may be the setting. Someone going into a church and saying, “You gillible idiot theists should be dragged kicking and screaming into the fourteenth century” is different from yelling it on a street corner. Going into a Godfather forum and saying, “You gillible idiot Godfather lovers should be dragged kicking and screaming into a High School Musical marathon” is different than saying it in a piece of art you created.
If you’re referring to Serrano in particular, I don’t think he’s a performance artist at all. Performance art is really a more specific thing than ‘procative artwork.’ (On that note I shouldn’t have mentioned Damian Hirst, who’s probably doesn’t count either.) It may be trite in some circles to go after Christianity but it’s also the dominant religion in the West, so there could be issues worth considering.
That sounds a lot more like trolling, although since it’s made up I don’t know what the intent is.
Andres Serrano is also a Christian, by the way.
No it isn’t, if it keeps your side honest. The biggest disservice you can do to your side is to not call it on it’s own bullshit.