Saeviomagy
Adventurer
All I did was give an example of why I personally would not associate with someone that was evil.
If other players in your group that are all playing evil/neutral characters that have no issue associating with someone that is evil there is no problem.
The guy I knew in college was not a cackling evil madman, he never harmed me or anyone I personally knew. He was still evil and deserved to be in prison and I would not willingly associate with him.
So lets start with the fact that 'evil' is a game term that is far too broad to be applicable in the real world, or potentially even in D&D (but that's another argument).
We'll continue on with the fact that you're using an association fallacy IE: "John has red hair. John likes motorcycles. Therefore all people with red hair like motorcycles".
It's certainly within my imagination for there to exist D&D-context evil people who cannot be distinguished from good people by their actions alone. The only time this comes up will be when an in-game effect that can determine alignment (which are actually very rare) affects them. There's even different degrees of that: as someone pointed out - much of D&D places you effectively in a war zone with high stakes. If party members A & B are both alongside you slaughtering orcs, then are you going to drop party member A because he enjoys it while party member B finds it distasteful but necessary? It's different if party member A starts fights with orcs that are unnecessary... but that's boiling over into the region of chaotic stupid, rather than evil.