Classic Straw Man argument – that is not what he said Matt. He has not “concluded” there is no god from this fact, he was responding to a very specific claim (by theists) about the wonder of nature and how that must ‘prove’ the existence of god. He says at the very first that he doesn’t know why we’re here! All he is saying is that the wonder of nature would (should?) be a lot less unpleasant for many living creatures (humans included) if it actually had been designed by some kind of all loving god rather than just evolved in the way that he understands

2) why is the humanist bothered by a life form doing what it has evolved to do?

I can only assume from this statement that you have no actual idea what it is to be humanist, or you are simply deliberately misrepresenting it to try and make your point. To be humanist, by very definition, is to care about other humans – just without the fear of reward/punishment for doing so. So of course a humanist cares about organisms that inflict harm and suffering on other people. You can still be amazed at how some parasitic creatures or deadly bacteria/viruses evolved while at the same time trying to help stop them from wrecking death and misery on other human beings!

I don’t see how from this specific quote you could derive the notion that Attenborough has chosen to be a nonbeliever because of the existence of parasitic worms. He doesn’t even allude to such thing. What he finds “difficult to accommodate” is that a parasitic worm speaks just as much to a wonderful creator as a hummingbird (which is the implication of this specific theistic argument).

As to why a humanist would be “bothered by a life form doing what it has evolved to do,” I’m a little stumped. What is it about secular humanism that precludes such a sentiment? How does intellectual assent to naturalistic evolution preclude an atheist from not wanting to get infected by a parasitic worm? Help me understand your logic.

there is the question of why “god” would allow such a thing. there is another question of why the humanist in a “godless” world is bothered by nature being nature.