You seem to have absolutely no idea how many people just died away in those times. You need food and health care, nobody will just give that to you. It will be survival of the fittest again, much more extreme then what we have today.
You seem to assume that everybody will have enough of everything and we all live in happyness and joy, only doing what you love.
That's of course BS. You will be fighting for your survival and chances are you'll lose that fight. Only thanks to our civilization it is possible at all to sustain that many people.