You need to sort your stepson out. If he is abusive towards women now, what will he be like in a few years if his behaviour is not corrected? You have a ticking time bomb on your hands, how will you feel if he abuses his partner in a few years time? If you feel your husband is not supporting you, you need to contact the authorities - kick up enough fuss until they take your stepson's behaviour seriously.
Your comment that he is fine around men and bad around women clearly shows he has not forgiven his mother. This is a classic child reaction to a parent who, for whatever reason, abandons them when young, especially if they are of the opposite gender to the child. I had a housemate years ago whose father had died when she was five, as a result she had a huge chip on her shoulder towards men in general and was unable to form non-abusive relationships (with her as the abuser). As with your child, she needed help from a psychologist to sort her views out. (Incidentally, when the child is the same gender as the parent who left them, anger is more likely directed towards the individual rather than the sex as a whole.)
Needing to see a psychologist is not weak or an illustration of a failed human being. Mental illness needs appropriate treatment, just as a physical illness does.
I think that, not being biologically related, you have a much more dispassionate and realistic view of the child's actions. If you are concerned about him, there is probably a good reason. Trust your instincts, and don't rest until his behaviour is properly addressed, for the sake of his future partner(s). You don't want their blood on your hands in a few years time.