I am pretty sure that if some fan went and made Adam Savage fan shirts, doing the screen printing and design all themselves, he'd be absolutely chuffed to receive one in the mail.
There's a difference between fans making and selling stuff because they are fans, and large corporations mass producing and selling stuff. One is largely OK in my opinion, the other not so much. This AT-AT model is an expression of love for the franchise first and foremost.
> I think lawyers would argue that by knowingly allowing some to violate your copyright you're left with less legal standing when others do the same.
IANAL, TINLA, etc.
Copyrights aren't quite as strict in that regard as patents and trademarks, but OTOH what's being violated here is primarily trademarks (an independent recreation of the appearance of an AT-AT in model form doesn't necessarily violate copyright in the way that copying or modifying 3D files and producing models from them would), and doubly so if the models are actually sold as "AT-AT Walkers" with or without the "Star Wars" brand.
An independent recreation like this is definitely a derivative work under copyright, but derivative works are often permitted under fair use. Whether this use would ultimately be permitted by a court is unknown, but a case can be made either for or against it, which is why any lawsuit by the competent folks at Disney would largely rest on the clear trademark violation, with the copyright claims thrown in for good measure just to drive up the legal costs; and since the fair use angle is definitely arguable you can't characterize it as a SLAPP and you can't really fault Disney for being willing to argue it in court. Vigorously, and at length.
Anyway, all this is besides the real point, which many many people over the years have learned:
There's a difference between fans making and selling stuff because they are fans, and large corporations mass producing and selling stuff. One is largely OK in my opinion, the other not so much. This AT-AT model is an expression of love for the franchise first and foremost.