A Critique of the Milgram Experiment

I have a few issues with the conceptual basis for what the Milgram experiment trying to accomplish.

His proposition - as far as I understand it - is that our society and its people are vulnerable to be manipulated by authority and we can easily be made act against our personal moral code to commit inhumane crimes against others. We let go of our personal responsibility when someone else is telling us to push the button.

But my issue with the experiment is it only works assuming that:
1. the subject is intimidated by authority
2. the subject is deluded by a plausible right cause

Here's what I mean:
1. A person who opposes authority would not want to be told what to do, regardless of the ethical implication of the task. The orders to obey would not work on him. It's not the right or wrong of the task that's relevant, is that he hates being controlled. Probably wouldn't sign up to participate in the experiment in the first place.

2. A person who is not participating in the interest of science, but simply to get paid, is not coerced to act against his own ethics. He don't give a fuck what happen to the other man in the first place. The assumption is made that humans are all inherently "good", then the proposition bases on those grounds. Whether human nature is "good" or "bad" is not really something you can prove. Why would people in positions of authority give the order to inflict suffering in the first place, if people are inherently good?