Matt, back in my “embracing” days I took communion at Protestant churches too. In fact, I came “that” close to registering at a Protestant Church as a member (while, of course, going to Sunday Mass too) because I was sure it would be perfectly fine and we were all ‘one’ anyway.
Now, I regret that I took that communion. . .not because I think ‘less’ of the people in that church (who are all still my friends!) but because in doing so I actually, in thinking I was being all ‘unity-minded’, was tearing Christianity down by acting and speaking as though it was something it is not. Christianity is not “truth A for this group” and a totally opposite ‘truth B for this other group’. It isn’t a question of “I understand the teaching to be X and you understand it as not-X but it doesn’t really matter provided we all are looking for God in ‘our own way’”. And by taking that communion, as a known Catholic, I was saying falsely, “this is acceptable to me, this is as valid to me as Catholic communion, this is the SAME.” And it isn’t. And in claiming it is we are keeping people from the truth, Matt. Instead of leading them to truth, we’re driving them away!!!