3d printing is theft. You wouldn't shoplift a toy, so why would you print it?
When the court system decides that Samsung can't make a phone that looks sort of like an iPhone, it's a good bet that courts will find that it's illegal to print, or assist printing of, a replica of some $megacorp object or part.
You know the part and can replicate its look... why not?
You wouldn't steal a cake, so why would you bake it?