They have never been problematic; the problem only comes when bigots make someone else's relationship their business.
That’s what made, and still less frequently makes, interracial marriages problematic. I didn’t think I’d have to state the obvious, but so be it.
The military used to require pre-marital counseling and permission from one’s commander and perhaps even still do, particularly between citizens and non-citizens; this JP isn’t the only one who makes a relationship his business. I don’t agree with what this man did, but if he’s a man of conscience, I support his right to act upon his principles (and suffer reasonable consequences), especially as he did no harm to the couple. His constituents will take care of the situation.