Barely. But you still can't keep up with the math. If only 3% of men each have 4 wives, that's a little under 12% of women taken, meaning that (again, roughly) you've just turned 9% of your male populace into those "unsuccessful, angry, embittered men with no attachment to the future". That is dangerous, not least for women.
Given that most single moms had their child with a father who would be unable to financially support multiple wives, I would doubt that we would see a significant decrease in single parenthood. Regardless, my answer to that stays the same - falling off the horse on the left does not justify falling off of it on the right.