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Second addendum...

alexandra_k: people are more likely to harm when they are instructed to harm by a person wearing a white coat and saying 'the experiment requires that you must go on'.

This is only true if people interpret a "white coat" to be a symbol of superiority and authority. Remove the white coat -- the symbol of superiority and authority -- and replace it with something else (a clown's nose? a sweatshirt? a fisherman's vest?) and people present with a different response.