Doesn't stop it being a natural occurance. And in the example you give, there's a measurable harm when applied to human mating (hence why it's generally not a good thing). There's no measurable harm in homosexual sex.
Mesuraeel harm has nothing do do with it being natural or not.. which is the point of this discussion.
But, let's dwell into this, shall we?
What is "mesurable harm"? And who mesures it? Who defines what is harmfull?
Obviously, the spiders and many other creatues KNOW what will happen but they do it anyway.
So obviously they consider that it is worth it and not harmfull for their species.
You can say - it must be harmfull as soon as a result someone dies!
Well, everyone dies as a result of life. Everything dies, it's just a matter of how and when.
so dying while doing something you like isn't exactly what I would call harmfull.. LOL