Don't confuse race with ethnicity. Ethnicity is a broad term to describe a group of people that may be categorized by a shared background, heritage, language, and yes, even religion. Race connotates black, white, Asian, etc., whereas you would share ethnicity with those people by not only being a fellow Jew, but also a fellow American. Yay!
Actually, you might find its etymology even more ironic, albeit outdated:
The term "ethnic" and related forms from the 14th century through the middle of the 19th century were used in English in the meaning of "pagan, heathen", as ethnikos was used as the LXX translation of Hebrew goyim "the nations, non-Hebrews, non-Jews."
Hmmm. Ok, in that case, I have a bunch of ethnicities, one of which is Jewish. Ditto for everyone in my synagogue, no matter what race. I'll have to get used to using ethnicity that way, though. Meanwhile I'll probably stick with describing us as sharing a religion and culture. (With due respect to the differing cultures of different types of Jews, lol.)
Thanks for the etymology of 'ethnicity.' Interesting! Just to clarify, 'goy' doesn't refer only to non-Jews. Goy just means 'nation' in general. The people Israel--all the Jewish people, I mean, not just the state of Israel--are also a goy. We're supposed to strive to be a 'goy kadosh'--a holy nation.
Colloquially, however, your quote is right: it usually means non-Jew in the singular, and in the plural ('goyim') it tends to mean the non-Jewish world. (But sometimes it means all the nations and peoples of the world, including the people Israel.)
(I bring this up because sometimes people think 'goy' is an insulting world. It isn't. You can use it with an insulting sneer, if you're not a nice person, but the word itself is neutral.)
Anyway, regardless of why things turned out the way they did, I don't see what purpose this serves on the whole; Of course religions won't teach about other religions on church time, their primary goal is to convince people that they have the right ones and that they need to focus on the religion they're in. It makes perfect sense; churches aren't just places of faith, they're a business, as well. If you don't have customers/a congregation, you don't have a job/a flock to guide on the right path, so to speak. They don't need to reconcile or compare, they merely need to keep their own numbers up and keep spreading the good word about their own faith.
Not all religions are missionary religions, so not all 'spread the word.' And I think religions do a better job now at coming together; we have a lot more interfaith dialogue and cooperative projects as far as food banks and things go than, say, sixty years ago. Plus many of us live in pluralistic areas, so people tend to know people of all different religious backgrounds. We've got a long way to go, but I think that as far as greater understanding between people of different religions goes, there are reasons to be optimistic.