I think the revolt you'd get from trying to move everyone back to subsistence farming (and also getting conquered by some other group who didn't do this) also means we don't know how to do that successfully. You're ignoring that last word again.
Protip: Read right up to the end of the comment before pressing reply. You missed a whole lot of context by rushing to respond midway through.
What I'm saying is that "knowing how to do something" requires knowing how to actually implement that solution, how to get people to agree to do it. You might as well say "we know how to get to tau ceti".
Did you not read your own comment? It already said that before.