I’ve never heard a plausible account of someone solving the is-ought problem, I’d love to check it out if people here have one. To me it seems structurally to not be the sort of problem that can be overcome.
I find subjectivism a pretty implausible view of morality. It seems to me that morality cannot be mind-dependent and non-universal, it can’t be the sort of thing that if someone successfully brainwashes enough people then they can get morality to change. Again, I’d be interested if people here defend a sophisticated view of subjectivism that doesn’t have unpalatable results.
Good point—this sort of worry seems sensible, for example if you have a zero credence in God then the argument just obviously won’t go through.
I guess from my assessment of the philosophy of religion literature it doesn’t seem plausible to have a credence so low for theism that background uncertainties about being confused on some basic question of morality would be likely to make the argument all things considered unsuccessful.
Regardless, I think that the argument should still result in the possibility of theism having a larger influence on your decisions then the mere part of your probability space it takes up.