For those who say compromise, Catholic and Protestant are not really able to do that any more than Jew and Hindu.
According to the Roman Catholic Church, a Protestant is not supposed to take communion or receive any Sacraments unless and until they convert to Catholicism. Likewise, Catholics are really not supposed to "worship" in another Christian demomination. The Roman Catholic Church considers sacraments received at Protestant churches to be invalid, and I'm pretty sure it goes vice versa, too.
The Roman Catholic Church was the original Christian faith. Protestants broke away. There are reasons for this, and those of you claiming to be faithful and bound up in your religions shouldn't need an atheist, albeit an ex-Catholic one, to explain it to you.