We are already constitutionally protected against everything 591 purports to protect against. Enacting superfluous law necessarily creates future risks and hazards.
Consider the US Bill of Rights. While the Anti-Federalists and Federalists argued positions, respectively, for and against a Bill of Rights, each with great reasoning and valid concerns, we have witnessed that the Bill of Rights, merely by existing, has been misconstrued to enumerate the only rights possessed by Americans. It may reasonably be argued that, had no Bill of Rights been enacted, we would have had no recognized protections. However, I believe that, had defenders of liberty kept focus on the blanket liberty assured by the Constitution, rather than allowing the focus to be placed exclusively on the Bill of Rights, we would have protected liberty in general, rather than merely the rights in the first ten amendments. That is, by concentrating our defense of liberty in specific rights, we relinquished general liberty, to the point that most Americans genuinely believe the first ten amendments are our only rights, and consider even those to be mere privileges, to be rescinded at whim. Our sorry battle, as a result, is protecting what few rights we focused on from direct assault, with general liberty long-since relinquished and forgotten.
591 creates a presumption and establishes an expectation, intended or not, that if a national "standard" for background checks is enacted, Washington will de facto enforce national "standard"-compliant universal background checks, or at least will be expected to enact such compliant laws†. Moreover, it creates a presumption and establishes an expectation, intended or not, that Washington's gun laws defer to the federal government. Furthermore, every law which is enacted carries not merely the risk, but the guarantee, of unintended consequences and misinterpretation.
However benign 591 seems today, it will prove to be a thorn in the side of liberty before long, simply by existing.
† 591, paraphrased, says, "No background check laws in Washington stricter than a national standard". 591 supporters think this is very clever, since there is no national standard. 594 supporters see a clear, one-step plan to get universal background checks in Washington. When, in the shockingly near future, there is some law that can vaguely be construed by a liberal judge to be a national standard (due, inevitably, to the complicity of McConnell-style Republicans), 594 supporters will say, "Hey, you said as long as there was a national standard, we could have universal background checks in Washington." Before you can begin to mumble, "That's not what we meant," they will have ceased listening to you, and you will have no credibility in the eyes of the normative voter.
