There isn't actually much risk in marrying a cousin. It is when successive generations marry cousins that you become more closely related to your cousin than yo

There isn't actually much risk in marrying a cousin. It is when successive generations marry cousins that you become more closely related to your cousin than you might naively expect. This is where the inbreeding risk comes from. And, parts of the aristocracy did, in fact, have significant effects from this inbreeding.