Quote From: agoodheart  
I just recently got married and I have a 12 years old son and my husband as a 12 years old son and to me they're different. My step son as an attitude problem towards his dad, his sister ( 16 yrs old ), me and my son. His dad won't punish him only do the simple thing and that is verbal. Talk to him but it hasn't done any good yet. He won't even crack down on him for anything. His son is in counseling plus on medicine. He has no feelings about how his dad feels, his sister feels, I feel or even my son. His son is in Martial Arts. My husband thinks that will teach him "self respect" then that way he'll respect others. To me, I think it'll just make his son get a little violent more. Thinking, "wow dad got me in Karate". He pushes a lot of buttons to for attention. He doesn't like my son or myself here. I moved out here moved back in my house letting my husband deal with his son for now. I won't move back until my husband gets his son to except his dad's "new marriage" here and having another child around.  
I have to disagree with your problems with the step-son being in martial arts. I've never seen a child that become more violent because of matial arts training, and in fact, many who have developed that self-respect, and self-control to control their violent tendencies.
If you have concerns about step-son's behavior, then take it up with the Sifu, Master (the name varies by discipline), basically the head of the School or Dojo he is taking lessons from. They have run into this concern before, can let you know what they do to make sure it doesn't happen, and take the time to stress the lessons of not using martial arts for anything other then self-defense and the protection of those weaker then they are.
If the teacher does not show interest in you over this, then find him a new school, but do not take him out of the one thing that may actually channel his behavior in a more positive fashion, give him physical activity and provide a sense of accomplishment for him.