The Democrats changed longstanding Senate rules to prevent Republican filibustering of Obama nominees. This is certainly majoritarian, but the whole point of custom and constitutions is precommitment. You’re designing rules for a game where sometimes you’re in charge and somtimes you’re not; there are limits on majorities that are agreed ab initio because you don’t know if tomorrow you and your group will be in the minority. Thus, everyone benefits by limits. But the Democrats abandoned those limits, both the customary ones, and the formal ones. Now the Republicans control all three branches of government, and the entire party recognizes the gem that is Neil Gorsuch: a thoughtful, articulate, and eminently qualified jurist of the Scalia persuasion.
As a matter of pure politics, the Democrats probably shouldn’t fight on this hill. They’ve lost the claims to any sacredness of the rules, having earlier up-ended them when it was convenient to them. Why not extend it to Supreme Court justices too? With Republicans united as they are on this, and disabused of any notions of reciprocity due to the tone of the Obama years, one way or another Trump will get Gorsuch on the Court, and the Democrats will face a more unfiltered and less controllable GOP majority, at least for the next two years.