Dude, they created the whole of the Sun for Men's benefit. That's a big thing, the whole of the Sun.

Huh? You're saying the Elves and Valar themselves didn't benefit from the existence of the Sun? It was an altruistic action? I don't buy that. The Sun was even instrumental in fighting against Melkor - without it, he would have been able to destroy the Moon.

Not to mention that they would never have done it if Melkor hadn't killed the Two Trees. They would have been happy to sit in their closed garden forever and let the world rot.

As for the first fall of Men, Tolkien leaves it deliberately vague, so we can't know how much they were to blame.

Whatever the Men themselves did, the Valar are to blame for leaving them to Melkor and Sauron.

Sauron made Orcs out of Men (or out of Elves in other versions), and these Orcs then became Melkor's and Sauron's soldiers for millenia. Orcs are, to put it mildly, not leading a happy life. Do you seriously suggest that anything the first Men may have done made them deserve the punishment of becoming Orcs? Did their descendants for all eternity deserve being Orcs? Did the Valar ever try to help latter-day Orcs, or just kill them on sight? For that matter, did the non-Orc descendants of those first Men deserve being "corrupted" for the sin of their ancestors? It's a Catholic Christian story, and it's unambiguously evil.

Incidentally, the story related by Andreth does say what the Original Sin of Men was: sacrificing to Melkor instead of sacrificing to Eru Iluvatar, and falsely believing that Melkor was their creator. Boo, they believed in the wrong god.

And after Melkor was defeated, they raised Numenor out of the oceans, and increased the lifespan of Numenoreans to like three times the normal amount, also ensuring that there would be fair weather, their ships would never sink, etc, etc.

Yes, as a reward to one small group of Men for fighting on the right side in the war and for sending a messenger to shame the Valar into fighting too. Pity they left the other >90% of Men to suffer on the mainland, though, with ordinary lifespans and Sauron.

Both the expulsion of the Noldor, the fall of the Numenoreans, and I can assume the first fall of Men as well, all those times where the Valar seem to abandon people to their fates, it seems to be when these people deliberately rebel against the Valar's authority

In the First Fall of Men, they didn't rebel against the Valar. They didn't even know the Valar existed! They woke up and all they knew was Sauron and Melkor!

And what about the Dark Elves? They chose not to go to Valinor, but they never knowingly chose to remain in lands dominated by an evil Vala. If they'd been warned about it, they probably would have chosen to go to Valinor. And yet, not only do the Valar never go back to help them, but they don't allow them to sail to the West themselves from the Grey Havens.

The Valar seem to be only able to help people when people acknowledge them as authorities.

It's nowhere stated that they are restricted in this way. (They are the regents of the world, after all, not of Valinor.) Rather, it is implied they choose to be that way.

Andreth argues that Men aren't supposed to die, that it's a great darkness ahead of them that they correctly despise and recoil from. Finrod, though disagreeing, is sympathetic throughout -- and I can't imagine that the author disagrees with his attitude in this.

OK, I agree. The author is sympathetic with "wanting not to die". He's just not sympathetic with actually not dying.