Can’t fault you on your use of a natural law argument, but will question its notion that we have a known purpose, as it confuses purpose with nature. A spider’s nature is to consume insects, but that’s not its purpose any more than our purpose is to consume a beer. It presupposes the existence of an agency that designed purpose into both us and spiders, and that the agency created our species to have duties towards the agency. It makes assumptions all over the shop, which is fine if we accept them, not so hot if we don’t. It’s no better or worse than any other system, they all rely on us having faith that their (often big) assumptions are correct.
Inocente:
I can see why several posters herein have been having problems with you: you either do not read other’s posts, or you immediately spin them into strawmen.
If you’ll go back an re-read my post you will notice that I said nothing about “consuming insects” being the spider’s
purpose. That, as I said clearly, is his
nature. Otherwise, what, then, is his
nature? To build webs? To scare little girls, minding their own businesses, eating curds and whey? To serve as models for low-budget horror movies?
Two questions: (1) What is the spider’s
nature? (Nature: that/those trait(s) (or aspect(s)) that is/are peculiar to spiders; that we dematerialize when we humans universalize the abstraction of spider-ness from the lot of them.) And, (2) what is the spider’s
purpose? (Purpose: that/those reason(s),
raison(s) d’etre, for which the spider exists.)
Then, I have two more questions for you (you can’t get off the hook that easy!

) (1) What is
human nature? I know you must have heard the expression: numerous times, more than likely. And, (2) What is the reason why humans exist? What is our
raison d’etre? Are we the only extent physical object on this planet without a purpose? And, if you answer, “Yes” to this, you must then explain it.
Everything humans build or make, we build or make for a reason, a purpose. Everything nature builds or makes, she builds or makes for a purpose. Every natural thing that builds or makes, builds or makes for a reason or purpose. Even if our knowledge is insufficiently broad to know what some of those reasons/purposes are, they are there and can, with a little bit of scientific investigation, be found out.
Now, if you come back to me and it is clear to me that you did not re-read my previous post, or, you attempt to strawman any of the above, I will refuse to spend another minute posting to you. Sorry, there are just too many meaningful posters and too many meaningful posts, in these fora. I don’t have time to waste. If you’re OK with that, respond. If not, don’t respond: I’ll take the hint.
God bless,
jd