OK, so, your point is that any man, even the worst man, is better than a single mother.
One thing I'm not sure of, however, is that women with the "I can do it all" attitude and their sons have absolutely no other male figures in their lives or would reject such a figure. I'm thinking a grandfather, a teacher, the father of one of her son's friends could make up even a liiiitle bit for the permanent absence of a man in the house.
I can only imagine that boys will seek the company of other men in other environments when they don't have it at home. It's not enough, but it's still more than nothing. And I don't think the "I can do it all" mothers are that crazy to deprive their sons of such interactions on purpose. Are they?
One thing I agree with you is that no child, under no circumstances, should be or feel forced to "step up", "man up", "grow up" or whatever, before their time comes. The parent, be it a man or a woman, is the one who should be and stay in charge at all times.