I would disapprove of 1st cousin sex.... but if both people are willing, and obviously consenting adults......... it would depend on your relationships with each other.

Are you close? like brother/sister close? if yes, I would say "GROSS" no way.

If you're not - and both of you want it......... well, its up to you.
If you're looking for APPROVAL, you're not going to find it anywhere I would think..... but I might get close by saying, if both people want it, and are ok with it, and neither of you have moral issues with it............................................. then do what makes you happy.

Personally, I object to 1st cousin sex.... If you were cousins a little further down the family tree line, distant cousins for example - that might be a different subject.