Probably the biggest 'lethal weapon' for anyone interested in such pursuits is - just enough knowledge to do something stupid.
A box of matches in the hands of a "firebug",or a casually discarded cigarette.
Back on topic:-
I'm very dubious about how useful in a direct sense 3D metal printing is.
The idea of heating steel dust with a laser doesn't instil a lot of confidence in me,as far as strucftural integrity is concerned.
If you can control something like the "metal spray" devices they used to rebuilt worn out crankcase journals back in the '50s,you might get results similar to cast or forged parts.
Of course,even those required a solid,if worn,metal part to rebuild.