What happened in 2007 was simply wrong (although an appointment happened in spite of it). The Democrats were plainly guilty of obstructionist tactics. It was partisan politics, plain and simple.
But the real point there is that they did not block nominations, suggested to the President that he should not nominate, and eventually consented to the appointment of Justice Alito.
And that's the difference in this case. Mitch McConnell is not only saying that the President shouldn't nominate, he's saying they should make no move to do their Constitutional duty to "advise and consent" or not give consent. He's saying they should block and not consider any nomination at all.
So it's really a different scenario.
And even if it weren't, what are we dealing with? Are we dealing with petulant third-grade students who don't know any better, or are we dealing with adults who should be able to say to themselves, "You know, two wrongs don't make a right"?
The Democrats were wrong in 2007. Does that really mean the Republicans should get a little payback at the expense of the Supreme Court, the American people who rely on the Court, and the integrity of the Constitution?