Personally, I find incest to be pretty gross.
However, if adults want to have consensual sexual relationships with their close relatives, I think it should be legal.
I'm a little more against inbreeding, since there is an increased risk of genetic abnormalities there, but even that I don't feel strongly enough about to make it illegal.
And let's not forget that certain kinds of incestuous marriages are legal in the united states. It's legal to marry a second cousin anywhere in the country. There are several states where you can legally marry a first cousin without restrictions. Rhode Island allows uncles to marry their nieces under some circumstances.
It's all just a matter of degree.