I've played a few shades of grey type characters over the years to varying degrees of success. My feelings have sort of shifted with time. I used to dislike the encouraged black/white, good/evil, etc. dynamic. As time's gone on though I think it's actually important because in my opinion it's what creates the shades of grey that come up in intrigue oriented rp.
What I mean by this is that... People will hit concept walls. I'm sure lots of us have seen it. A player who has some grand idea for their character that we know is ultimately going to get stonewalled. And that sucks. But often when I see that happen it's because of the approach. Things like people with no subterfuge skills like Bluff/Perform for example who want to do lots of inbetweener stuff or characters who want to literally bring peace between the surface and the underdark forevermore or somesuch. Once you understand the social dynamics a bit better though I think the binary approach encouraged at the macro level makes characters who operate in both realms more interesting. A character who moves, even just relatively freely, between the underdark and the surface is interesting precisely because of the obstacles they're overcoming to make that possible and there's a whole world of unseen roleplay that's essentially these characters juggling different interests to achieve their outcomes even for simple things like just being able to move freely.
That's not to say that things couldn't be better. A lot of people get really invested in rp that might ultimately not be able to pan out the way they hoped and I think there's conversations to be had about if a better balance couldn't be struck. It's no fun for example to be the character who's about to be banned from literally everywhere because they just wanted to learn about their enemy a little so they chatted with one. But I think that designing some degree of obligatory separation between the surface and the ud is good because it creates room for a lot of interesting rp around subverting that separation which would otherwise be superfluous in the broader rp landscape.