Males should not be forced to have vasectomies. The decision to procreate is one that belongs to the individual, and if a man wants to be able to father children, then he should have that right. Forcing men to get vasectomies is akin to forcing women to have their tubes tied. There is also the question of how society would go about deciding who would comprise the 2/3 of the men forced to get the vasectomies and why.
Forcing two thirds of the male population to get vasectomies would have huge ethical and health concerns. For starters 2/3's of the male population would be less likely to use contraception which would lead to an increase in sexually transmitted diseases. Also in that two thirds we may eliminate a portion of the gene pool that could have immunities to various diseases that science may one day be able to learn from. Finally what ethical way could society choose to force 2/3's to be subject to this vasectomy.