Marrying your cousin.?

Why do so many people think marrying your cousin is wrong? Just because it scientifically says there's only 3% higher chance of birth defects- which Is nothing. Before this entire scientific BS many people thought of it as normal like albert Einstein, Edgar allan Poe, etc. How is it disgusting, especially if you hardly seen them? Oh, && BTW it's not . I'm just asking for opinions not RUDE answers because ur not going to make me change my mind, thank you. In many countries it's legal, even in 26 states in the US, I bet ur ancestors have done it too. LOL