nanning,
Your familiar with the quote that " sufficiantly advanced sciences appear to be magic".
The newer one is that sufficiantly advanced technology appears to be biology.
Check out Helion Energy for a simple and modular fusion engine is in buildout phase. Fits in a boxcar, and uses magneto accelerated plasmas to impact with each other. They then use thermoelects to pull off electricity. You could mount one in a ship. Or a spaceship.
Luddism is only for 20 something's. Baby's, adults, and old folks need healthcare, lights, heat or cooling. And we will need bio reactors and 3D printing to offset material shipping, and manufacuring foods from algae.
If you want simple tech, change your focus to get rid of patents, and turn to asteroid mining for materials. People will keep inventing tech and med, but we need to optimize on best design, modular construction, and recyclable materials. Asteroid mining and lunar ISRU, can teach us to shovel in mine waste, or river siltation, or even landfill waste, and get back separated base materials.
There is a great group doing open source, simple design, robust and modular farm tech, think it's Open Source Tech, or something. Tech can multiply horsepower, and reduce damage to ecosystems more than simply reducing population back to 500k humans...