[William McKinley]

Incest as a non-violent sexual practice among consenting adults is constitutional

I do not think you are going to find widespread agreement and acquiescence on this point.

[RipSawyer]

"Incest as a non-violent sexual practice among consenting adults is constitutional."
"I do not think you are going to find widespread agreement and acquiescence on this point."

If not specifically forbidden in the constitution it is allowed, where is it forbidden? Cite the exact wording please.

[GraniteStateConservative]

Argue that it isn't. The 4th and 5th amendments assume we have a right to privacy (though the pro-choicers have used it for abortion, which is inapplicable since the unborn child has rights, as well). Even The Federalist Papers were published anonymously. The government has to show a compelling interest and there isn't one for the act itself.