Jo

Strolling into a synagogue eating a ham sandwich (assume that it is an Orthodox synagogue and that you are a Gentile and that you are legally permitted to be on the synagogue's property) is bad and you should not do it, because it is rude and disrespectful, and hurting persons' feelings for your own amusement/convenience in that way isn't justified.

Doing a kiss-in to protest in favor of gay rights is good and you should do it, even though the entire point is to shock, horrify, and disturb people, in a rude and disrespectful way. 

So what's the difference?

I think that the difference is that in the former case, you're doing it just for your own amusement or convenience, whereas in the second case you're doing it to actually accomplish something that makes the larger world a better place. 

Perhaps inconveniently, this would mean that strolling into a synagogue eating a ham sandwich is morally justified if you are genuinely doing it as an act of protest because you really strongly oppose the traditional Mosaic prohibition on eating pork. (If you're doing it just because you like stirring up trouble and offending people  –  and who doesn't enjoy that  –  then you're still an @$$#ole.)