We did that in philosophy at school (that was one of the few subjects I liked!) and yes, it disturbed me, too. It shows how readily people do anything if they only can say "I had to!" or "They told me to do it!".
If I remember correctly, people accepted it best when the people who told them to push the button wore uniforms or medical attire, because that made them authority figures. People are always ready to clear their coscience by blaming others, even if it happens subconciously.