Is it fair to not like someone because s/he slept with someone you don't like?

Inspired by @ronski’s recent question, my question is kind of the opposite: is it fair to not like someone because s/he slept with someone you don’t like/don’t respect/think is disgusting/basically think is an ass, etc, etc… For example, you are totally digging on a new guy or girl and then you discover s/he recently hooked up with someone you can’t stand. Could you/would you still like the person you had a crush on? Will your opinion of/feelings for someone change based this kind of information? Would you judge them? For the sake of this question, let’s say you have discovered that the object of your desire had a short-lived relatoinship with the person you can’t stand about six months ago.