It really depends on the masquerade and the people involved. Blowing the whistle on something like the wizarding community in Harry Potter, for instance, would be of seriously questionable morality given that while any witch or wizard is potentially dangerous to muggles only a comparative few actually are and those are criminals...to say nothing of the fact that the masquerade is so extensive that trying to unveil it would ultimately be fruitless and practically suicidal due to the inevitable retribution that would follow.
If we're talking about a much smaller and far more dangerous masquerade, then you're hitting more interesting territory. Chances are still good, however, that both sides would want me dead if I revealed its existence. Humans because I was a monster, my 'kin' because I just performed what was likely the single gravest sin by their standards.
If it's not obvious, I lean more towards upholding the masquerade unless I was convinced that its destruction was both a possibility and worth sacrificing my life for.
If we're talking about a much smaller and far more dangerous masquerade, then you're hitting more interesting territory. Chances are still good, however, that both sides would want me dead if I revealed its existence. Humans because I was a monster, my 'kin' because I just performed what was likely the single gravest sin by their standards.
If it's not obvious, I lean more towards upholding the masquerade unless I was convinced that its destruction was both a possibility and worth sacrificing my life for.