著名无神论者，如劳伦斯·克劳斯和理查德·道金斯，曾表示支持乱伦。他们认为，只要性行为发生在两名自愿的成年人之间，就应当被允许，即使是母子、父女或兄妹姐弟之间。

Prominent atheists, like Lawrence Krauss and Richard Dawkins, have expressed their support for incest. They argue that as long as sex is between two consenting adults, then it should be permitted, even if it’s between mother and son, daughter and father, or siblings with each other.

这是世俗伦理学中一种常见的模式：打破禁忌。通奸曾被视为不道德的，但世俗伦理学告诉我们，那只是一种非理性的禁忌。鸡奸曾被视为可耻的，但世俗伦理学告诉我们，那同样只是一种源于情绪而非理性的非理性禁忌，因此是无效的。

This is a familiar pattern in atheistic/secular ethics: taboo breaking. Fornication was always seen as immoral, but then secular ethics tells us that that is just an irrational taboo. Sodomy was always seen as vile, but then secular ethics tells us that that is just an irrational taboo born out of emotionality rather than reason and is therefore invalid.

和同样的思路也适用于与直系亲属发生性关系的情况。

And now the same thought process applies to sex with immediate family members.

为什么无神论者这种习惯性地打破边界、冲破禁忌的做法要就此止步？是什么阻止我们把“同意”这一观念也看作一种由情绪驱动的非理性禁忌？同意与其他已被抛弃的禁忌有何不同？一位无神论者或世俗主义者可能会主张：正如落后的人曾认为鸡奸是一种恶心、反自然、亵渎神明的行为，同样，落后的人也非理性地相信，未经同意的性行为是一种令人作呕的侵犯；而在这两种情况下，都没有理性或科学的理由去遵守这些过时的禁忌。