Every bloodline has recessive genetic mutations, when people who are related bang it out the child is significantly more prone to have these defects. Even if both parents are entirely healthy and don't have the mutation themselves, they still hold the gene responsible for the mutation to be passed on. I get that you're not supporting incest but when you say stuff like that a pornbrained incel is gonna see that and use arguments like that to support their weird beliefs. But yeah, people do tend to like people that look like them a lot more due to many factors (familiarity factor, genetic markers that signify health or compatibility, other stuff like cultural influences)