"It would also remove posts from any state in which a gun seller says a background check will be skipped, even if such checks arenâ(TM)t required where the seller lives."
There is no law requiring such a check in most states, therefore they are knowingly deleting posts which conform to the law. What's more, it is essentially impossible for a private citizen to perform a proper NICS check, meaning that it is impossible to honestly comply with the intent of the policy.
Also, it requires a near expert in law and firearms to determine which guns are actually legal or illegal, so there is little chance of this being implemented as intended.
Finally there is little evidence of a positive causal relation between background checks and actual impacts. While we can certainly accept that sometimes it may offer a minor deterrent or slowing, in most of the incidents which have led to this type of policy implementation it would have absolutely no effect, thereby negating the need for such policy in the first place.
This is a TERRIBLE situation.