Up to 60% or more! https://xkcd.com/870/

Maybe that could be a legitimate source of revenue for free-to-play games, if it was a consensual agreement. Gamers typically have high-performance hardware, so why not use excess capability while playing a game, as long as it doesn't interfere with gameplay. Sure, cryptocurrency is generally not worth the electricity it wastes to produce. However, it may be a better alternative to ads or traditional payment schemes.

I feel like anyone who is afraid of "3D-printed guns" has never: (1) used a 3D printer; (2) shot a firearm. Regulating things without understanding them has always been the hip thing to do, but this is silly, because it will never be prevented through regulation.

This, 100%. From the images, it looks like they are building 0.5-1m thick walls with internal structure that emulate the structure of cinder blocks (maybe 30% infill). They are also embedding some thin wire as they lay the concrete, but I don't see how that's going to do much, especially since it's not affixed in any way to the other layers. For a three story house, as shown in their renderings, that seems somewhat suspect. Maybe the Netherlands have loose building codes.