I agree. There's nothing "don't ask - don't tell" about it. This whole subject has [needlessly] caused a lot of confusion in the gun community. As States began to "legalize" the medical, and then recreational, use of marijuana many people lost focus of federal law. But no matter what state law was, marijuana continued to be illegal under the Controlled Substances Act, and anyone using marijuana continued to be an "unlawful user of a controlled substance" and therefore prohibited under federal law from possessing a gun or ammunition. The confusion on that point is obvious to anyone who has read the enormous amount of hogwash posted on the subject on gun boards.
The 2011 ATF letter was an attempt to make things clear for FFLs. The recent change to the 4473 is an attempt to make it clear to persons buying a gun.
So to be clear:
Anyone who is a user of marijuana, even if legal under state law, is violating federal law. He is an unlawful user of a controlled substance and is therefore prohibited under federal law from possessing a gun or ammunition. If a user of marijuana answers "no" to question 11e on a 4473, he has answered falsely and thereby committed a felony under federal law, in addition to any other federal crimes he may be committing.