Re: fooling around b/c divorce is hard, I really can't speak to the issue b/c the only ones for whom it's socially stigmatized and also a hassle are the Orthodox, of which I'm not one.

Re: religious versus ethnic, religious Jews uphold the Sabbath, oftentimes keep kosher, go to synagogue often. Ethnic Jews may or may not celebrate holidays, usually do but may not go to synagogue (but will get together with family) might go a few times a year to synagogue but not more than that. Still, they identify as Jewish b/c their families are Jewish and they live differently than you do. You could never set foot in a 'gog again and still be Jewish, and not just because a lot of Jewish ritual happens at home and not in the 'gog.

For every holiday, new moon, sabbath, etc., there are a number of ways to participate. Ethnic Jews, if they participate at all, sort of skim the surface of possibilities. But they'd feel the sting if they were dissed for being Jewish, just like an Orthodox would. There are different types of religious Jews. There is one type of ethnic Jew.