Is a character acting entirely in a self-serving manner really "good" just because the best course of action for them happened to save lives?
Allow me to rephrase: Are you really *not* evil because you're only helping someone to get yourself cured?
I think the issue a lot of you are having is that you're conflating evil with "join the goblins and the Absolute." Sadly, Larian perpetuates this misunderstanding by describing helping the tieflings as good and helping the goblins as evil. An evil character could quite realistically (as many have said) be convinced to help the "good guys" to get themselves cured.
Or perhaps the issue is that joining the Absolute more or less requires the sort of psychopathy of chaotic evil, when most people appear to be approaching this with a more lawful or neutral evil mindset. You guys are being self serving, and are willing to do evil acts to further yourself, but you're not recklessly destructive, seeking to do evil for no other reason than to do evil.
Mind you, this is still a problem that should be addressed, in my opinion. Joining the Absolute is not currently an appealing option in the slightest, and I think if not for Larian telling us they wanted people to play as evil this go around, fewer people would have done so naturally.