Well, even atheists set limits to what they can do in sex.
That is a sign that they don't really believe in total liberties in sex provided you can get away with it because no one knows about it or at least legally you don't get in trouble with the law.
But since atheists don't admit of any transcendental morality or decency for humanity, that is an inconsistency in their setting limits to sex.
In effect they do maintain a transcendental morality or decency for humanity.
For animals who do not have the same nature of man, there is no questioning morality and decency with them from us humans and to all appearances they do what their nature moves them to and they can do so, even though for us humans some behaviors of theirs can be for us humans immoral or indecent or perverse.
So, for human there is transcendence in man's nature.
And with animals and no condemnation on them at all, their nature does not include any component of transcendence.
Yrreg