Here's what is said if they refused to pass it.
Them - "Why, those eeeeeevil Republicans are refusing to even just extend a law that bans guns that can be snuck past metal detectors."
Us - "Well, we have an absolute right to guns, um, even ones that can go through metal detectors and that no one has any plans to legally make."
Ma and Pa Kettle, who don't -care- about gun rights per se but who we -must- have voting with us or at least not against us on gun rights - "Wait, what? Why on earth do you need invisible guns? Maybe you -are- the loonies."
Them - "(snort) Those idiots had us on the run but they chose to hand us the rope to hang them in the media -and- kicked themselves in the nuts over what is objectively an absolute non-issue in the big picture, given current politics."
There is zero upside to fighting a clean extension this go-round. By passing it, the Dems will look like the extremists for asking for idiotic expansions, which will put their vulnerable on gun members in danger for supporting them, and look like the unreasonable ones for not "compromising" by accepting an extension.
It's possible to win -and- be right, there's no point doing things the stupid way for no possible actual gain.
Bah. Gun control is a non-starter politically, despite your fantasies. Dems will take no losses by asking for more, GOP would not have taken losses telling them to stuff it. Pretty much like the 1994 AWB.
GOP and NRA: Always ready to bugger their constituency to please the left.