Western thought is against racial/ethnic loyalty. That is why westerners do not like the fact that Judaism inherits membership based on blood. I happen to support ethno-nationalism as a theoretical concept, therefore I have nothing against Jews wanting to preserve their ethnic identity, just like I would have nothing against Spanish, Italian, or Russian people doing the same thing. If two liberals want to marry across ethnic lines, they shouldn't do it in a Jewish state of course, and they shouldn't claim to be upholding religious tradition while they do it. Perhaps what annoys me is people who claim they are being observant Jews and intermarrying. It's the dishonesty. If people intermarry and admit they are not following Judaism, then it doesn't annoy me as much.
While I think ethnic preservation is a good thing, attempts to say "it is just religion" are simply dishonest, there is an ethnic component too. Christians, Muslims, and Buddhists do not assign membership based on birth. Only Hindus and Jews do.