Taken to the logical extreme, self sufficiency is 0% efficient. You cannot have it both ways.
Communities, and then cities and then empires grow when you divide and conquer - which could have been the strapline for Adam Smith.
they made everything they needed including their shelter from scratch
That is a brave statement when I explicitly asked "and the tools to do it ?". Did they make the screws ? The nails ? The pipes ? The bricks ? If not they were still just making an extreme IKEA kit and only cosplaying being self sufficient.
Even the earliest colonists to America were not self sufficient - they had to take things they had not made (tools etc) and even then would never have survived had they not traded with the indigenous people.
And there we come back to where were are today. We trade to buy food. and what we need so we can make what we want.
When I saw David Cameron back in 2009, it was almost his catch phrase - he must said "we are a trading nation" every other sentence. To a total tumbleweed from an audience that had been primed to ask about immigration.
The very bottom line is I don't feel like paying for other people to fail to achieve food self sufficiency in the same way I don't want to pay for flaky energy like windmills or non starters like reviving the high street.