This is your friend's twisted way of validating himself. There isn't much that you can do to show him that this is a result of his own low self-esteem (which, by the way, I think you hit that nail right on the head). This problem is unfortunately very common. You cannot solve a problem if you see no problem at all.
Outside of himself, the only one(s) that can make him see the err of his ways is (are) the woman (women) he's dealing with. You see, you are looking at a co-dependent situation here. These women have low self-esteem as well. Many of us have suffered from it, and many of us still do. He preys on those women who are seeking companionship, then exploits their weakness for his own satisfaction. No woman with high self-esteem would allow this to go on for an extended period of time and unfortunately, many of us are still on our journey to that goal of higher self-esteem.
This cycle will continue indefinitely until either 1) he meets "Fatal Attraction," 2) he meets that one woman who knocks him off his feet and persuades him to change his ways, or 3) some miracle occurs and he sees that his actions are not only destructive, but also self-destructive. The problem is...there is no problem--at least as far as he is concerned. Until he can admit that there is a problem, he will never have a reason to face it or change in any way. As long as he is satified with his actions and the results, he will never admit there is a problem. Nothing matters to him right now except self satisfaction, so the feelings of these women mean nothing.
It's obvious that you do not like the road your friend is taking. My advice to you would be to separate yourself from the situation as much as possible. I'm not saying separate yourself from your friend, just from the situation. Let him know that you are not pleased with his activities and that you don't want to hear anything else about his escapades. Whether you know it or not, you are being disrespected as well by being subjected to behavior of which you disapprove. It is completely up to you what you will tolerate in a friendship. We are often drawn to people who are "like" us. You have to decide within yourself if this is someone with whom you want to associate yourself.