Not really sure how Mohammed can be said to have a "dubious" history. If you don't want to believe the traditional accounts, that's fair, but late antiquity was not a golden age of objective recorded history lol, so there isn't much better info to go off otherwise. I would refer people to r/AcademicQuran on issues of early Islamic history.
I can't say whether Smith had a "dubious" history, but I'm not inclined to take this view because people think it's ok to bigoted and dismissive of the Church of LDS, and I think it's unfair.
Also polygamy was part of pre-Islamic Arabia, whereas it was contrary to custom and law in the context in which the LDS Church developed. Comparison on this point is superficial.
I can't say whether Smith had a "dubious" history, but I'm not inclined to take this view because people think it's ok to bigoted and dismissive of the Church of LDS, and I think it's unfair.
Also polygamy was part of pre-Islamic Arabia, whereas it was contrary to custom and law in the context in which the LDS Church developed. Comparison on this point is superficial.