I mostly want to call everyone's attention to two excellent posts, by Brian Beutler and by Ryan Grim, which take seriously a key fact about the gun bill consideration: simple majority votes on amendments would have not only allowed Democratic amendments to pass, but would also have allowed Republican amendments to pass. In particular, the Grassley substitute, backed by the NRA, received 52 votes. But I'll do a little speculation and thinking about reform options from where they leave off.
As they both point out, in a simple-majority environment, things might have been different. It's absolutely possible that Democratic defectors might have been willing to hang with mainstream Democrats if their votes were needed -- any whipping on amendments surely went into the close Democratic amendments, not the GOP items.
This is not, in and of itself, a reason to oppose Senate reform in general, or even a majoritarian Senate in particular. But as I said before the bill came up: reformers should be clear what they want.
For example: in a Senate with very loose controls on what bills and amendments come to the floor; with one tightly disciplined (or ideologically rigid) party; and with simple majority voting on everything, then the tightly disciplined party might do very, very, well over time. Even when it's in the minority, even when it's in a fairly significant minority, that party shouldn't find it hard at all to get its way on many, and maybe most, bills.
Moreover, that minority party would have strong incentives to act as tightly disciplined as it could. After all, in a 55/45 Senate, if the minority can figure out something that can pick off six majority party Senators, they get to win as long as they all hold together. And as long as there are loose controls over the floor, they can design whatever they want with that goal in mind.
The obvious recourse for the majority, in that situation, is to eliminate opportunities for the minority to offer amendments. Otherwise, they risk simply get repeatedly rolled by any smart minority willing to hang together.
In other words, it's very easy for reform, once it starts, to wind up where the House has wound up -- with a majority party quasi-dictatorship.
Again: that doesn't mean one should oppose reform. But anyone who thinks that majority party rule in which the minority cannot participate meaningfully in governing, including offering alternatives which can receive votes, is some sort of obvious democratic system is overlooking some very real problems with that kind of system.
At the same time, anyone who is happy with a status quo which requires an arbitrary 3/5 supermajority for everything, and thinks that such a system is obviously the democratic one, is at least just as wrong if not more.
What remains unclear is whether it's really possible to get a third alternative -- one that gives the minority party meaningful participation, and which allows intense minorities (whether they are partisan minorities or just minorities on some issue) to have real chances to succeed against indifferent majorities.
To be sure, there are reasonable arguments in favor of majoritarianism and against that third alternative, but in my view they are losing arguments (as are those favoring the 60 vote status quo). But if it isn't possible to design the third alternative, then it doesn't really matter whether the theoretical arguments hold or not.
Still, I think the arguments about democracy are important and worth keeping at center stage during these debates. It's simply not true that democratic theory would consider a pure majority-party-run Senate to be necessarily the most democratic. You can argue it, but you need to do so, from where I'm sitting.