Are you a machinist? I don't understand why you'd dismiss 3d printing and say metal is more feasible to work with. 3d printing is much more accessible to the average DIY-minded person.
I think this is cultural or location based – I know at least a dozen people who can weld and no one who has a 3-D printer, but I live /way/ out and rural America. The Internet would suggest that urban America is the reverse.
Sure, but if we're talking about replacing machine parts, I'm not sure how far welding will get you. You need to be able to machine custom metal parts, for parity with basic 3d printing capability.
You can bend small metal pieces with your bare hands, or with pliers, or you can beat it into shape with hammer (or any stiff object). Plastics get damaged and break when you try that.