'Failure to protect' a child from injury is why so many mothers are blamed for their children's misery in adult life. This holds true whether or not the mother is even aware that the child has been assaulted. 'Failure to protect' might also be the reason for many men's hostility to women in general.

If a mother allows her son to be sexually assaulted, wouldn't it follow that the son would feel anger toward his mother and generalize that feeling to all women?

Aside from the fact that it is not a medical necessity, I think that there are many psychological and emotional considerations. In fact, I think it should be considered a crime. I don't think too many men ever gave their consent to be circumsised.