What makes us dislike so passionately?

I went for a walk to a beautiful nature reserve near my house this morning, a fly was buzzing round my head and getting way too near my face for my liking.  I brushed it away, while thinking what revolting insects they are, it dawned on me that I wouldn't have had that thought if I didn't associate flies with really negative images implanted in my mind.  From squirming maggots to starving children with flies settling on their weeping eyes and open sores, all those images have played a role in polluting my mind so deeply that no matter what role flies have in our eco-system, I hate them!
On a similar vain, despite knowing I'm being totally illogical, I have had the experience of feeling wary, nervous and wanting to end a meeting when in the company of someone with  the same hair style, or general appearance as someone who has hurt me or let me down in the past!
So, it's one thing to be uncomfortable with an insect that does indeed spread infection, and quite another to allow the headmind to be scarred by a life experience that results in being catapulted back to that memory when meeting someone who looks like the perpetrator, or wears the same after shave!  If you have had a similar experience, then the moment you notice your headmind taking you off to a different place and a different time - STOP!  Do a reality check on the situation you're in right now, and remind yourself that THIS is a new and unique experience.
"The past is never there when you try to go back.  It exists, but only in memory.  To pretend otherwise is to invite a mess." - Chris Cobbs
"Memory is deceptive because it is coloured by today's events." - Albert Einstein