While the reforms are targeting those who should not be in possession of firearms, they also target firearms specifically.
They would outlaw all magazines in excess of 10 rounds, and renew the "scary-looking weapons" ban.
While this legislation isn't a push to ban all firearms from all people, there is a group which mirrors the real gun nuts. They use the passage of common sense laws to put in submarine "discretionary" language, which allows one person, or maybe a handful, to effectively remove large swaths of firearm ownership if they can get supporters into those positions.
It's the submarine subversion by the extremist left corollary to the extremist right which makes those of us who are not extremists very leery of any legislation. It only takes one bad apple to spoil the whole bunch, and it's hard to make sure none of those bad apples get into positions they can abuse. It's easier to try and prevent them passing any legislation which might be subverted, since extremists cannot be trusted (and I mean extremists of any stripe, including pro-gun extremists).