If you assign specific seats to specific individuals, what if someone doesn’t show up? Then you’ll have unrelated married opposite genders sitting next to each other.
And do you really leave no-shows seats empty?
What if an unexpected guest comes? You might not have a space to stick him/her in where he/she is not sitting next to an unrelated married opposite gender.
And, really, once the seating is mixed, even if you assign specific seats, is no one gonna sit in a seat there not assigned to? Of course it will almost always happen. And you will have men sitting to next to unrelated married women.
And socializing.