I think one underlying thing that bothers me about it that this is an ex-slave town, who pretty much all desire to make it to the surface one day. Good "dark" makes me think they're embracing the enviroment they're in, and that's just meh.
I think you are over estimating the human psyche. Humans are made to adapt and accept their surroundings, both physically and mentally. A good example of this is capture bonding.
"Fighting hard to protect yourself and your relatives is good for your genes, but when captured and escape is not possible, giving up short of dying and making the best you can of the new situation is also good for your genes. In particular it would be good for genes that built minds able to dump previous emotional attachments under conditions of being captured and build new social bonds to the people who have captured you. The process should neither be too fast (because you may be rescued) nor too slow (because you don't want to excessively try the patience of those who have captured you...")
In essence, this is what has happened in Sanctuary on a massive scale. People have formed new bonds, new attachments, and have built a new community. This is all built upon the fact that many are former slaves, or know someone who has endured slavery, giving the people of the city something to bond around. It is a shared experience in which they can all relate to on some level. This bonding is further encouraged through the many trials and tribulations they face as a community, forcing the people to bond even more closely in order to survive.
Oro summed up how most, if not all, my characters viewed the Seekers and how I believe they are perceived in general. Certainly, the city is filled with people who would rather be living on the surface, but 98% of those people realize that it is nothing more than a pipe dream.
Even if you are filthy rich on the surface - even if you are a king, there is no point in returning. By the time you return there would be someone else on the throne, your valuables and wealth divided among your kin - who are more than likely not willing to give it all back. To those you left behind on the surface, you're dead or missing and while they may have waited the first two weeks or so, hoping against hope that you'd return - they've moved on with their life - putting you behind them as nothing but a memory.
That's the reality of being trapped in Sanctuary, and I'm sure most people who come from the surface, especially those who have been in the Underdark for more than a month, realize as fact and truth.
The Seekers only keep a dead dream alive, a tiny flicker of hope in an otherwise dreary and forlorn existence. They are the naive optimists in society, the folk all the rational people love to hate.
...and speaking of hate. I really don't understand all the hate toward the phrase "Good Dark". It's a greeting as well as a goodbye, similar to Aloha in Hawaiian. After 150+ Years such people would have already developed their own slang and cultural identity.
But yeah, anyway - Strife I think it's safe to say that Sanctuarians ARE embracing the environment they are in, it would make little sense for them to do otherwise.