Do I make my own bread? Sure, sometimes I do. Baking bread isn't that hard. But do I do it every day? No. Why? Because it takes time to do, my kitchen counter is usually a mess afterwards, and the result usually doesn't taste anywhere near as good as the 20+ bread varieties I can buy at the corner store. I sometimes do it for fun, but I wouldn't do it every day.
Let's go to macro scale: What's the better solution: 1000000 people each baking their own bread (1 loaf a day), or a giant company baking all the bread? A million stoves are most certainly less energy efficient than the professional industrial ones at the company. Having to divide the resources into many small packages and distributing them to each individual households is less efficient. The quality of the bread will vary widely. And lets say baking takes 0.5 hours, that's 57 person years wasted per day to do something the bread factory can probably do with a few dozen employees.
The same argument advocates monopoly or central planning by government?
If not, you have to jistify where is centralised enough. Now, if we have a 20,000 different bakeries, is that actually centralised?
Decentralisation of plumbers doesnt mean everyone does his own plumbing, it means anyone willing to learn can become a plumber and there is no plumbing monopoly.
Also we should debate the actual subject, not debate it indirectly throufh analogie, it just introduces an extra step of inaccuracy and cultural baggage.
But it is more about the problems than the methodology. Centralized/Cooperative methods are more appropriate to solving a complex problem for which you know the solution (building a house, mass transit, maintaining highways). Distributed/Competitive methodology is better for exploring a problem space (determining the most energy efficient house design, innovative bus or train engines, cost effective highway surfaces). If you use cooperative when you should be using competition, you get a cartel. If you use competition when you should be cooperating, you get extreme inefficiency and long delays (I don't think we have a word for when we force groups who should be cooperating to compete with each other for resources).
I agree in terms of forcing, but we have plenty of ways to describe the general idea of choosing this direction, typically in exchange for a (real or perceived) benefit, but almost always with the inefficiency/delay you mentioned:
homegrown
homemade
handmade
handcrafted
artisan
DIY
roll your own
My argument isn't "centralization is good no matter what".
My argument is "centralization is not inherently a bad thing that is to be overcome. Done correctly, as demonstrated by many existing systems in our society, it is a great way to make things our society needs work at scale in an efficient manner."
Decentralization like democracy introduces inefficiencies but at the same time provides safeguards against these conditions. The goal is to provide the minimum amount of inefficiencies while providing the maximum amount of safeguards.
Most democracies are not purely decentralized systems, however. There is still a central government, the difference is how it obtains its ruling power.
Even the elections themselves are not de-centralized, as in "everyone run his own DIY election system and we'll see what sticks". There are central authorities for tallying votes, providing election sites, safeguarding and vetting the process, declaring rules, etc.
Which is a perfect example for how cenralized systems can be both efficient and safeguarded.