See, I'm in the Pathfinder wrath of the righteous alpha, after playing the evil route in it. I disagree. Alignments provide a framework, it also helps the writers remember there are various forms of evil rather than being a teenage murder hobo. For some reason, the game with alignments and where it's a common complaint that it's restrictive, has for more nuanced decisions and ways to roleplay an evil/good character than the game that got rid it by WOTC's order.
Larian wanted alignments, WOTC said no. The whole point of getting rid of them was the complaint that it's too restrictive, yet in this event we got a basic, boring evil path with no incentive, no setup and the only people it will please are those who just like killing people or who want to have sex with the drow. So much for getting more nuanced characters and writing after being free from a "restrictive" system. This is just my opinion after playing both.
I don't see how alignment has anything to do with it. It's just a matter of how good of a writer are you.
If anything the Pathfinder alignment system forces writers to come up with stereotypical things an aligned character must say, PF:K is full of these for instance. Forcing players into predetermined tropes and in PF:K's case even going so far as to change your alignment if you are too good or evil is very restrictive.
That being said, yes; the current evil path is like this because it is so pointless. People do it out of obligation to the goal of this EA or for drow boobies now. An alignment system would not solve that and racial / class / religious dialogue is far preferable to it but some kind of morality compass needs to be there, especially for pragmatists. When the Gith creche is released this could be an interesting "evil" choice, to just forego the central conflict of Act 1 and go your own way. So long as there is no "you left the refugees to their fate and both sides died because of your apathy" ending slide later.