You've nothing to fear from 3d printing, it's far more challenging than you would think. If your settings aren't perfect, or you use the wrong plastic, or a single failed layer adhesion point occurs because someone breathed in it's direction at the wrong time, can turn your plastikov into a pipe bomb.
No, I'm not exaggerating. An errant draft from walking up to the printer in motion can ruin adhesion, and you won't know it until you're pulling hunks of pla out of your bleeding stump.
Yeah, I've seen it. What you're missing is the guy has years of experience, a perfectly calibrated printer, and in spite of that, the device WILL fail eventually. You have to use either polycarbonate (which requires a lot of modification and a heated printer enclosure, but is a little too soft and will distort from repeated impacts), or pla, which is rigid enough to not distort during use, but pretty brittle and has very poor thermal tolerance. You can make up for some of that with carbon fiber infused filament, but that stuff releases into the air during printing, and is highly abrasive to both your hotend and your lungs.
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