Do nonbelievers intellectually resist this?

Yes

No, that's just another self-serving lie from someone with an agenda to push.

It doesn't work for me, but I can see it working for someone who hangs around with a lot of depraved people.

While the quote is true, so far as it goes, it is also true that humankind can be remarkably compassionate and caring towards others.

It is, in fact, the unavoidable, unresolvable dichotomy of human nature.

We find it hard to recognise our own sin let alone the fear based mental illness that drives it ,it has developed over 3 million years we are used to it , Buddha and Jesus developed treatment few really use it.

It is a fun hypothesis for the shut in who isolate himself from his fellow humans, it becomes more untenable with every human interaction.

Yes.

How would you empirically define depravity?

I don't care about it at all.