Yeah its not a good idea to associate a whole group of people because of one person, it doesnt always work out like that.
But its human nature to do so.

Imagine you and your friend are both cavemen who have seen a Tiger for the 1st time.
It looks a bit scary, but you approach it anyway.
Then it bears its teeth and eats your friend, and you run away.
Lesson learned - Tigers = Bad.

Thats the instinct for survival.
unfortunatly modern culture isnt as simple as that, and prejudice doesnt always work.

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