https://m.youtube.com/watch?v=X9bULArrKs4
^^Ian explains the wonder that is the Zip 22
One legal argument against them hinges on how you interpret the Fifth Amendment's "shall not be deprived of life, liberty, or property without due process of law" bit. Generally, "due process" refers to a trial, like one in which you get convicted of a felony and lose your right to bear arms. Red flag laws deprive somebody of that right without a trial (granted, on a temporary basis, but the point stands).
You'd think that Jews of all people would support the right to bear arms, given their experience at the hands of a German state that systematically disarmed its citizens before killing them.
Some of them do: http://jpfo.org
Here, if you're okay with a mid-length gas system. Aero is absolutely the best bang (heh) for buck for uppers.
Your considerations for a SHTF gun might differ, but I built mine primarily considering weight (lower, better) first, then role versatility (e.g. use a 16" barrel which won't excel at any ballistic function but do fine for most purposes).
Why do you specifically want a carbine-length gas system?
Feel free to make a darkweb site for us. Will nevertheless point out that we post nothing here that justifies the hassle of running unindexed.
If you worry personally about getting tracked, you can decently hide yourself by using a VPN, browser configured against fingerprinting (Brave, Firefox, etc.), and an open-source OS. Make sure also to encrypt your drives and physically disconnect your machines from power when you don't use them.
For maximum infosec, use Tor Browser on TAILS while connected to a VPN that's not your own or that you paid cash for.
Consider the Desert Tech MDRX in .308. 20-inch barrel goodness in a 30-inch OAL package. It costs a pretty penny, though.