3D printing and manufacturing might very well lead to a day when people can create their own firearms at home. Wow. Implications here are huge.
they can now with a little equipment
I believe some components could be "printed" but other high stress parts wouldn't be able to be. I don't think stuff like barrels, springs, hammers, firing pins or bearing surfaces would work well.
Metal parts can be manufactured with CNC lathes, etc or injection molded. These machines are getting cheaper and cheaper. Or you could just build one.
If someone is willing to pay for the machinery, all of this stuff can be built virtually using autocad, then fed into a 3D Printer/CNC setup.
There are additive manufacturing machines, aka 3D printers, that can make parts out of titanium and even inconel. The primary issue with additive manufacturing is the tolerances of the finished product. When metals are sintered they tend to warp and distort causing accuracy problems in barrels for example. It would be feasible to print a barrel whose bore has material left for a more accurate process.
I think a lot of the fascination stems from the fact most people are familiar with printers. A lathe or a milling machine is a foreign object. Grandma hears about 3d printer and she thinks its the same as the HP on her desk.