Anything is a social construct.

I don't know if you'd want to marry a porn star, and if not, that should tell you what he difference is. This is one of those things which is "freedom" in theory but has many second order effects in practice.

As much as I don't want to marry a porn star I don't want to marry a professional sports player. And you know what? Just because these people are allowed into a country doesn't mean the local residents want to marry them.(The reverse ironically works tho)

The point is either reject all of them or treat them all equally.

I'd have no issue marrying a porn star, but maybe I'm strange. But, regardless, we don't qualify immigrants but how marry-able they are.