The Church didn't seem to have a problem with the white-black anti-miscegenation laws that were in effect in the US until recently.
The Church says that it's not immoral for different races to marry, but seems to not have a problem with communities making laws against race-mixing.
Why else would the Church never object to those anti-miscegenation laws?
That's about all there is in support of anti-miscegenation laws. That the Church didn't oppose them.
But neither did She impose them.
Furthermore, She has blessed interracial marriages.
So, there is nothing in principle wrong with them. But, various places can make their own marriage laws.
Like how different States can ban drinking before 21, without the Church complaining. It doesn't mean that drinking under the age of 21 is wrong.
States can forbid teenage marriages too, and the Church would respect that right.
But, that is not tantamount to saying the Church forbids drinking or marrying under 21. And nor is the Church's non-objection to anti-miscegenation laws proof that the Church opposes miscegenation.
Because She Herself allows those things. If other places want to be stricter, then let them. They don't have to be.