So if this was a good deed, then I assume you would have to consider it a good deed for frum schuls to welcome Catholic worship as befits the needs of the Catholic faithful, replete with an altar to offer the Holy Sacrifice, statues, icons, Blessed Sacrement etc.
Yes?
Yes?
I said it was a good deed if they davnened in a hall with no acoutrements of idolatrous worship. I don't know why any Orthodox Jew would be willing to worship in a place full of idols. The hall isn't part of the church, is it?
The answer to your question is very simple. The chrstian bible contains the Hebrew Bible, so chrstianity acknowledges the licitness of Jewish worship. On the other hand, the Jewish Bible doesn't contain the chrstian "new testament" at all, so you can't expect Judaism to acknowledge chrstianity the way chrstianity acknowledges Judaism, can you?
Put even more simply (and starkly), since Judaism is the true religion and all other religions are false, then davnening in a parish hall and an idolatrous "sacrifice" offered on Jewish property are not at all comparable.
Since you're a newbie, I'll give you a little information: I'm not Jewish. I'm your typical Southern Bible-thumping redneck who eventually followed his beliefs to their ultimate conclusion in Noachidism.
However, I must admit that I much prefer traditionalist Catholics to the neo-conservative papolators who treat the 1994 Catechism the way Fundamentalist Protestants treat the King James Bible. Unfortunately, it is the latter type of Catholic who predominates on Free Republic (and if you're a true traditionalist who subscribes to all the ancient beliefs unchanged then it is they rather than I whom you need to worry about; they've run at least one Catholic traditionalist off this forum, calling him a Protestant and an anti-Catholic bigot). The only thing that I don't understand about traditionalist Catholicism is its hostility to Jews and Judaism, as if Judaism were merely another false religion like islam. How in the world do you label your own claimed proto-religion as false and offensive to G-d? 'Ekh!