I think our insincts are primeval, and we lack the skills to interperet our feelings, but they can often be proved right.
It probably dates back to prehistoric man who would instinctively be wary of someone from another tribe who may smell, look, or just 'feel' different, and i think this instinct is still with us.
For me, it even extends to people on TV - of whom I obviously have no personal experience. I am sure Alan Titchmarsh is really a perfectly nice guy but ...
I am a Scorpio too!