I'm assuming you meant "If a guy doesn't let the MOTHER of his CHILD see the son."
It all depends on the circumstances. If the mother is abusive, neglectful, or does not provide a healthy, safe environment for the child, then the father is doing what is necessary to protect the child. The safety and well being of the child comes first, always. The child may not be old enough to have the capacity to understand why he/she cannot see their mother, but in time as the children grow and mature, I'm sure they would see things more clearly.
However, if the father simply does not like the mother, and is simply keeping the child from her out of spite, revenge, etc., then yes, it is HIGHLY likely that child will eventually come to harbor a great deal of resentment toward the father. Just because the mother may do things the father doesn't approve of or agree with, this doesn't necessarily in and of itself mean that she is not fit to be in her children's lives.
Parents who are no longer together MUST be able to put their personal differences aside, and focus primarily on what is in the best interest of the child, and whenever possible, this includes the children having good, strong relationships with both their mothers and fathers, and the parents should do everything necessary to SUPPORT these relationships. It's unfortunate that so many parents are too selfish to put the best interests of their children above their own childish games, because the children are the ones who pay the price for all that nonsense.