However, in our current state, we're seeing the repercussions of this type of shift in western countries: vast unemployment. To me this means we just have way too many people alive now. Clearly that isn't a quickly solvable problem (unless you are a genocidal maniac or something...), and so greatly reducing the birthing rates over coming generations (which hasn't really even been approached yet) is the only solution.
A much smaller global population, with largely technologically optimized labor, is the only solution that really would allow most of that population to live comfortable lives in relative luxury.
So you can see how I would view any argument about what needs to be done in the short term as moot, as in my mind it would just be a waste of effort
If we can overcome resource and energy scarcity, I don't see why we couldn't support an arbitrarily large population comfortably. Unemployment is not a reason to downsize the population, it just means we're outgrowing or current economic system.
When, at any point in human history, has the world ever approached anything resembling "fair". The reduction in poverty and increase in quality of life in western countries has all come at the exploitation and subjegation of people in poorer countries. Certainly we've shifted the massive inequality from local to global, but just because you don't see it doesn't mean it doesn't exist.
Put another way, until we find some infinite, inexpensive source of energy and material resources, no one will live in relative comfort without many more being exploited. That is the way of the world