India seemed to be working perfectly well with "your current life is a barely relevant rounding error in the midst of aeons of torment and the best thing to do is to cease existing" being an extremely prevalent viewpoint. And the old blood-money practices are a rather major departure from your ahistorical farce of a glorified past.
The problem is thoughtlessly rejecting received wisdom without the legwork to replace it. Nothing more special than that, and there's absolutely nothing making secular humanism impossible to get as robust as the old religions.
And the moment the Problem of Evil comes up, the thing you're calling necessary as Christianity has it has its days numbered, because explaining it is monstrously excessive for the vast majority of people.
To say nothing of the horrid bullshit it introduces for distant foreigners and the pre-Christian world. The entire idea of "Virtuous Pagans" has zero scriptural basis, but needed to exist to not have the extremely vast majority of humans be fully damned solely by accident of birth, including the very people who handed down the ethical system that diverged Christanity from Judaism.
Funfamentally, Christianity is exceptionally poor under scruitiny, because it has too many trivial questions with absurdly complicated answers. "The divine is just Really Powerful rulers and/or embodiments of natural forces perfectly able to be unreasonable jackasses just like us" worked fine for the millennia prior to Christianity.