When there's no head, it's dead!

I just stumbled over someone's musings, but they made sense and finally allowed me to understand why Corran does not like Kyp:

Corran believes essentially that the Dark Side is just like any other criminal mindset. It effects only those who are already messed up in the head to some degree. As a police officer, there are just "good" and "bad people" to a certain extent.

So he would think that Kyp had a criminal mind which caused him to desire vengence and would make him always be corruptable.