The question is not about logical or illogical. This question is about law. It's all about faith not logic. You are free to accept or reject it.
Marrying first cousins is prohibited in Hinduism as far I know. The laws vary from society to society. Again anyone is free to accept or reject it.
And then,
Finally I enjoyed your sarcasm. It's not the question if govt should set laws established 1400 years ago or now. The matter is, in society you can't do whatever you want.
In ancient Egypt marriage between siblings were legal. Now if any govt want to make it legal too, and arrange a poll, you can vote for it I have no objection.Because although children born of incest will be defective physically ( Indeed this scientific logic does not apply on children between milk brothers and sisters.), but if any adult people enjoy consensual incest and decided not to take any offspring then their is no harm for them physically ( screw the social harm theory, since it's terribly backdated idea according to anti religious people ) harm so you can vote for it scientifically in order to reject old and obsolete laws that was established even 2000 years before
the famous 1400 years ( using this magical figure became a norm I see) , and their is also no perfect history ( is their any authentic history of prophet Moses who recieved covenant from God for Jewish people? People say the covenant was 3300 years old) .
So in order to abolish such old and unscientific logic and laws and establish a more modern and scientific logic, anyone is free to do so, also can start a movement legalizing consensual incest in any country ( since law against incest is not
1400 years old, but
3300 years old ) , and anyone can vote for this, I have no headache.
Finally in my post I just showed them the law is from Quran not only from hadees. I was not trying to say that everyone must abide by the rule.
The rule of Quran is only for Muslims, not for them who don't recognize it as the law of God! So in a society where Muslims are predominant, you can't ignore their rules and regulations when trying to introduce something that goes against their law. Same theory applies for other society too.
@bluesky