BS. Show me where any libertarian has ever said that.
What libertarians believe is that people have inalienable rights, and the function of government and laws is to protect those rights from the actions of others, and punish those who violate others rights. Statists, whether they call themselves "liberals" or "conservatives", believe government should outlaw anything they decide is "wrong", regardless of whether anyone's rights are being violated.
Thanks for making my point.
Libertarians believe what two consenting adults.....
And if brother and sister (brother and mother, brother and even father, whatever...) are of legal age, there should be NO LAWS against incest.