This is a short-term effect, and you have the fitness function backwards.
The portion of the population that takes action to avoid living in squalor is unfit because they fail to reproduce well enough for replacement. Meanwhile, the portion of the population that fails to avoid squalor is breeding in a most exponential way. That portion was historically kept in check by death, but now has been unleashed.
So one type of person is on the way to extinction, and another type is growing without bound. Currently this means the the total population (both groups together) is shrinking, but that will change.
The portion of the population that takes action to avoid living in squalor is unfit because they fail to reproduce well enough for replacement. Meanwhile, the portion of the population that fails to avoid squalor is breeding in a most exponential way. That portion was historically kept in check by death, but now has been unleashed.
So one type of person is on the way to extinction, and another type is growing without bound. Currently this means the the total population (both groups together) is shrinking, but that will change.