While hitting is a normal 2 year old behavior, I have seen some kids where it was extreme. One child was slightly younger than my DS, and I knew the family well. Of course we don't know what all goes on behind the closed doors of someone elses house, but I'd bet the farm that this family did not abuse their firstborn(or anyone). Their firstborn son was extremely agressive. He was agressive to EVERYONE. He was about 3 when they had a second son. He could not be allowed near the other child because he would hurt him, badly. His behavior got worse. They did consult a therapist and spent a couple years taking and attending therapy with the oldest.
Bottom line, they worked through the issues their oldest had and he went on to do well in school and life. Their 2nd & 3rd sons had none of those problems and also have done well. They are a great, and functional, family. The mom attributes the work with the therapist as being the most affective in their oldest son's life.
If a behavior is over the top, a consult with a therapist isn't going to hurt. Like everyone has said, 2 year olds hit; it's the degree that should be of concern. We can't tell that from a message board.
ETA, I mentioned my friend & her husband did not abuse their child because quite often an abused child will abuse others. I mentioned that because I'm assuming you are in the same situation, that you do not beat on people.
