Kentucky

Bill also reduces the penalty for diddling relatives from ... 12 years old onwards...

Do you have a moment to research the extinction of the Hapsburg family line?

In all seriousness, at face value, I agree — consenting adults should be able to do whatever they want. However, things get sticky when you introduce reproduction to the mix.

Charles Darwin was one of the first scientists to demonstrate the effects of inbreeding depression, through numerous experiments on plants. Darwin's wife, Emma, was his first cousin, and he was concerned about the impact of inbreeding on his ten children, three of whom died at age ten or younger; three others had childless long-term marriages.[14][15][16]

Wikipedia

If this was happening where I lived, I would care about the potential impacts on the community from the possibility of an increase in genetic disorders of children born from such a union. Including increased stress on Healthcare, increased mortality rates during childbirth, increased citizens on government assistance, etc. Not saying these things would happen, but I would care enough to look into it.

There's also the impact on reputation resulting from one of the states leaders thinking this was an important enough issue to create a bill for, and then the impact on reputation if it gets enough votes to pass. Would the opinions surrounding morality and / or reproductive rights carry less weight? Could it even sway people away from the side taken by Kentucky just because it is the side Kentucky is on?