Neville, I personally agree that it is important to preserve mesora, which is harder when there are mixed marriages and everyone goes to the same schools and learns the same things in the same way.
But there is an attitude that bothers me: when a frum ashkenazi gets engaged to a sefardi, even in the US, everyone has to comment about it and it’s not because they are worried about how the mesora might get messed up. I know of people who will avoid shidduchim with someone whose last names sounds sefardi, even if they are not. And there is a certain derogatory word for sefardim that is unfortunately bandied about a bit too much.
You are right that there is a double standard though. It is considered discriminatory when an Ashkenazi yeshiva does not accept a sefardi student, yet no one seems to notice that the sefardi who is begging to get into the ashkenazi yeshiva is actually discriminating against the sefardi yeshivos, implying that they are not good enough.