Trump's most fascistic act during his first term, so far as I can tell, was the bump stock ban. If you want to claim that you believe in democracy and that you want to live in a free society, you can't really support an act by government that threatens people with prison time that was enacted without a democratic process. The bump stock ban was was a Trump and the ATF passing a policy that threatened citizens with years behind bars, and that was done without the legislature passing a law.
The SCOTUS's decision wasn't that the government couldn't ban bump stocks. The decision was that the government can't ban bump stocks in that way.
Of course, the shocking thing is that the bump stock ban is the one relic from the Trump administration that the left passionately wanted to keep.
It's hard to reconcile support for our democracy while being perfectly okay with a government agency, populated entirely by unelected people, can throw people in jail.
This is far from an isolated problem. Dexter Taylor is serving a decade in prison for accidentally breaking an ATF policy. He didn't break any law that was actually passed by a legislature. The ATF has been trying to pass a policy that would throw people in prison for being in possession of a pistol brace. Again, there was no vote. The legislature was never involved. You know the Hunter Biden gun case? Again, it's a violation of ATF policy, not of a law that was properly passed by the congress.
Since the left is usually not gun friendly, and swaths of people care more about restricting guns than they care about how these restrictions get passed, it's not too surprising that this is a massive blind spot for them. Frankly, I don't care whether or not gun restrictions affect you personally. If you fancy yourself a Democrat and a believer in freedom, you can't also be broadly in favor of throwing people in prison based on the whims of an unelected government agency.