there would be a small organised millitia to neutralize dangerous stilllives

Yes, but the still lifes aren’t the only danger. There is still the time warps, instability of walls and flooring with the null zones, the bacteria.

And IMO contact with the backrooms clearly a induces a form of paranoid schizophrenia, as seen by some of Kane’s work.

So it would be an inevitable disaster to use the backrooms for any useful purposes.