To clarify for others not sure what the counter argument should be as an atheist, start by understanding that religion is not a requirement for morality and consciousness. You evolved to have empathy and respect for other humans as part of surviving as a social animal; you get along with others or you die. This also applies to animals to varying degrees, although culture tends to dictate which animals deserve respect.

In other words, the "golden rule" applies to other humans and animals within that definition and are granted as the same rights we want for ourselves, sexual autonomy included. That's why most of us wince at the thought of this faulty premise because that's the normal reaction, aside from it also just being gross.

"What about the bad people?" you might wonder, given you probably know a guy who would fuck roadkill. Well, empathy is an evolutionary trait, so just like any trait it'll vary, with some having no empathy at all because being a good liar is also sometimes a solution to society (it's just, less so since if too many select that route, the whole tribe dies).

Aside from that, humans form groups and prefer in -groups over out-groups. Typically this means you are more likely to cooperate and share resources with people similar to you because they're more likely to return the favor due to proximity, but it can also be manipulated by leaders to dehumanize whole groups of people, leading to all sorts of horrific treatment like rape and murder. Empathy doesn't factor in at that point.

Religion, if anything, is just another grouping factor that has been used to create such othering and dehumanizing of people, as history has shown for thousands of years and still happening today in places like Gaza. But back to the roadkill fucking; if religion is the only thing stopping you from fucking a dead deer, then there is clearly something very wrong with you, both from a moral lack of empathy for animals and from a sanitation standpoint.