Why is it considered incorrect to marry your first cousin ?

well it really is incorrect but I've read on other forums that in China parents prefers 1st cousin marriages so they can keep their clan's money :) well in Alaska they have this custom that before a woman can marry a man she must first be deflowered by her own father and in Germany they don't allow a woman to get married if they are still virgins I don't know if that's true or just a hoax :)

Because people think such is morally wrong and scientifically speaking, it'll cause genetical abnormalities to their child.

It depends on the society/culture, it's quite acceptable in many places and not causing any problems. cousins are not like brother and sister, usually they don't grow up under the same roof and many times they don't even live at the same neighborhood or city so there are a safe enough distance for natural love to grow between cousins when they come together.

Because not only are cousins STILL RELATED in most cases, and share the same BLOOD, but it's been proven that if cousins have a child together, there is over a 50% chance that they will have a genetic disorder, but they can also be slightly 'slow', too.

I agree that an intimate relationship with a cousin can happen. Society usually condemns a person for having a relationship with a cousin or a relative for moral reasons, eventhough in ancient times this practice is widely accepted. With the advent of religion, this practises are slowly being considered as taboo depending on what culture you are raised from. We have grown up in a society that has conditioned our minds not to make relationship with a relative.

its because often cousins marry cousins for generations and it can cause birth defects to show up more often. itshealthier for your children to have parents who are not already related.

Because of the blood relations. It is scientifically believed that marrying your close relatives will result in physical or mental abnormalities in your children.

yeah it can cause birth defects. anyway but ic ant imagine marrying my first cousin as he/she is like my brother ,sister. so anyway there is no thrill in taht marriage. marrying some1 u dont know really ahs soem thrill.