Nothing does that though. Old electric cars were built from donor cars, rip the ICE from a Volkswagen or something and then put in batteries and electric motor

Nothing does that though. Old electric cars were built from donor cars, rip the ICE from a Volkswagen or something and then put in batteries and electric motor. This is worse though, you're not building a car, you're building a cell factory. It's much more like bootstrapping a compiler. Now, it's possible to hand code the assembly to make your low quality compiler, that's just good enough to compile a subset of your language that'll let you bootstrap the full language. That's rough though. It's much quicker to just use C or something to implement the first version of the compiler, then implement the target language compiler in the target language. I agree, it would be cool to be able to snap together molecules to build structures. The best way to do that today is to use cells to make the molecules and snap them together. We just don't have little Mems devices (or whatever) to do that. Especially not in bulk. Someday, we'll have a device that's not a cell that can do what you want - it just doesn't exist yet. Cells are almost a magic cheat code, giving us access to building stuff we can't build any other way.