Reading these comments makes me dispair about basic understanding of the law and government's role in preventing "censorship" by a private corporation.
Question: Is a company engaging in censorship somehow violating the constitution or the law?
Answer: No. The Constituton limits the governments' actions. It is designed to protect the people from government infringement of certain delineated rights. There is nothing in the Constitution or federal law that prevents private corporations from expressing an opinion about the desirable use of their own products. Government may regulate certain behaviors (i.e., discrimination in hiring or health and safety), but is prohibited from picking winners and losers based on political belief. Corporations are subject to no such restrictions.
Question: Is it "illegal" for a company to revoke a lease because the lessee is using the lessor's product in a manner that the lessor thinks is disagreeable?
Answer: No. The lessor is a private company with rights to its own personal political positions and beliefs. There is nothing "illegal" about the company enforcing its contractual rights because it dislikes the use its product is being put to by this particular lessee. (Again, leaving aside certain lawful restrictions on a company's conduct). Instead, it is the terms of the lease that will govern the relationship between the parties.
Question: Is it legal for a lease to differentiate between political views?
Answer: It's very much up to the individual parties to craft a contract that governs the lessee's and lessor's rights. The point is that the parties have complete freedom to arrange the lease as they see fit. In fact, it is common for a lessor to include very broad re-take rights into the contract. If the lessee believes that the lessor has repossessed the equipment in violation of the contract, then he or she has rights under contract law, and the appropriate remedy is to sue (or not agree to the lease to begin with).
Question: Even if we assume it is legal to print a gun under federal law, the law of all fifty states and every local jurisdiction, does the legality/non-legality affect the rights of the lessor to repossess the printer under the lease?
Answer: No. The legality of the finished product has no bearing on the contractual rights of the parties to enforce the conditions of the lease.
Question: Does the 3-D printer manufacturer have legitimate legal concerns, even if the printed guns were unambiguously legal?
Answer: Absolutely. The manufacturer could easily be the target of a law suit for negligence on the part of a victim of the printed gun. The civil liability claims could be enormous. Even the potential threat of such litigation could raise his insurance premiums or cause existing insurers to rescind their coverage. Remember -- in America, each party typical pays its own legal costs. A law suit does not have much merit to bankrupt a small business. And here, the manufacturer was on actual notice that the lessee wanted to make a gun, which would help any plaintiff in establishing that the manufacturer knew or should have known that his product could be used to harm people.
The manufacturer could also be subject to some far-fetched legal theory advanced by a prosecutor in some random jurisdiction. Or he could find his product subject to import/export restrictions in the US or other jurisdictions.
PS - It's not clear to me what the law says on whether printing guns is legal. I'm a lawyer, and spent maybe 10 minutes reading a couple of the various rules. It was enough to determine that it's a complicated patchwork of federal and state rules. In anyone has a lawyer willing to say that such behavior is unambiguously legal under all federal, state and local laws, without any thought or research, should find themselves a new lawyer.
Summary: I'm trying to keep this post a-political and just about general legal concepts. We as educated Americans (or interested foreigners) really need to appreciate when Constitutional rights are at stake and when the Constitution has nothing to do with the underlying issue. This is one of the latter situations imho.
And yes - I am a lawyer - I am not your lawyer. So please don't rely on this posting for legal advise; merely commen sense.