Prophet Muhammad married due to socio political reason
You are talking about inbreeding ?
Dude islam has not allowed you to marry your sister
Take an example what if your cousin and you fell in love with each other
Marrying cousin is not considered taboo in any religion
It is allowed you are allowed to marry any muslim girl and even christian and jewish girls
If you dont wanna marry because you fear inbreeding then its upto you
Now if you have allergy with say onions you will sy why did prophet ate onion because it causes problems to my health
What dude use your brain sometimes