Medical people take an oath (I watched my wife take hers). For the vast majority, they are very ethical people sworn to that oath, and have decided on careers as doctors, pharmacists, nurses etc. due to a very real personal belief in helping people.
Some are rotten apples, but then again you get that in religion and business as well. Unfortunately there's no lie detector test to be taken before getting your cap doffed. These people do come out.
But it's best not to taint all people with the same brush.