They have pointed out in 2016 and now that if the Senate has the power to block a Supreme Court confirmation until after the election in an election year, then they are right in doing so. If the White House and Senate are of the same party in an election year, then they are right to proceed with a confirmation.
The problem with that argument is that logic would seem to require one to extend the "no confirmation" argument back two whole years--maybe even four. What's so hallowed about an "in an election year"? If there's a Republican president but the Democrats take the Senate in the midterm elections, couldn't they reasonably say, the very day after the election, "Well, the people have spoken; they've elected a Democratic Senate, and so we're not confirming anybody until after the next election when they have a chance to speak again"?
Of course. And in the current environment, Democrats probably would do and say this. The cycle will likely stop only if a party pays what it seems to be too high a price at the ballot box.
It's worse. One party will have to be willing to pay too high a price at the ballot box by doing the right thing. Their members will be primaries in favor of wingnuts, and they will lose to said wingnuts, a significant portion of whom will then go on to lose to their opponents in the other party.
The way to stop this is to hit the reset button and say "fine, we're sorry about Bork (or Garland, if we're going to wait another decade or three) -- we'll vote to confirm and stop trying to block your nominees."
The Democrats undisputedly started this. Republicans were undisputedly late to the party, but when both parties finally play the same hardball, the only way to end it is by calling a truce. A truce requires trust. Trust is earned. And trust may not be rewarded (that is, say the Democrats agree to play fair -- that is no guarantee the Republicans will).
About the only good news in all of this is we have at least 5 members of the Court who are conscious of their role as judges, the limited judiciary, etc. So maybe the Court will become less of an issue by osmosis as the Court moves toward a more Constitutional role.
I'm hopeful, but not optimistic.