I'm kind of ok with the incest laws as they are now. I agree that incest is basically acceptable (or, at least, nobody's business) as long as there is no coercion or power misbalance - so never between parent and child - but unfortunately I think most incestuous relationships do involve exploitation and power misbalance. I think the law needs to have room to be able to prosecute people for that.
It's kind of like the age of consent/15 years olds having sex with older people - the law is there for when it's needed, and for when there's been an abuse of power, but on the whole, when a relationship is harmless, there aren't really legal consequences, even if it's technically illegal.