I think that there are some significant elements in John's response to Elizabeth's request to the go to the authorities.  On one hand, John feels guilt about what happened.  Yet, John has already demonstrated himself to be very strong of mind and independent of how others perceive him.  In Act I, when Abigail throws herself at him, he rejects her and is quite strong about it.  He does not like being told what to do.  Therefore, his response in Act II becomes an interesting one.  In one aspect, he feels guilt about what he did and does believe to an extent that he should come clean to the authorities about it.  Yet, on the other hand, he simply does not want to get involved with any of it and wishes to remain distinct from it.  Additionally, he does not want to be bullied into doing anything because of the guilt that he feels from Elizabeth.  Thus, his response is a combination of both guilt and resistance.  He feels guilty in light of Elizabeth's view of him, but he also feels resistance because he realizes that his own sense of self is quite strong.  It is here where his emotional response is conflicted and uncertain, elements that prove to be dangerous in the social setting of Salem at the time of the trials.