As the genetics informed us, it is pretty common for all Ashkanazi descendants to be related.
Yes, there are Rosh Yeshivas and Rabbonim that married their cousins, but 1) ain somchin al haness, and 2) their kids might be fine because the gene is recessive, but they could ruin the lives of great great great great grandchildren. I wonder if you ask them if in 10 generations one of your grandkids will die young because of a genetic disease by marrying their cousin, what they would answer. Would they still marry their cousins?