There is a sentiment that men are more aggressive, more competitive, more warlike than women, and, therefore, less nurturing. While it's true that with a family of boys even the most innocent kitchen spoon can be turned into a deadly weapon, men ARE NOT not nurturing (excuse the double negative).
A boy can be nurtured to become a husband and then a father. And when that boy becomes a husband and father and understands his importance as role model, teacher, protector, leader, provider . . . he can be as nurturing as any mother.
People traditionally rise to the level of expectation that is set for them. Rather than encourage your boys to watch bumbling, violent, insensitive, disinterested examples of husbands and fathers in the media, provide higher expectations and find examples that show what a major part of being a man is about--becoming a good, nurturing husband and father.
Consider Muddling Through: Perspectives on Parenting by Bil Lepp for a great laugh, a good cry, and a better understanding of why fatherhood is important.