Nothing is being swept under the carpet. The simple truth is that allegations of electoral fraud wildly exaggerate the scale of it. If you are going to say that some fraud exists, then of course that is sadly true, but any reasonable estimate of the scale means that it is a handful of votes out of a hundred million that are questionable. That simply doesn't register in the way that Trump is either implying or directly saying will be the case. To pretend that he can't accept the legitimate result of millions of the American people because maybe a hundred votes (and yes, that is the right scale) might be fraudulent, that is indeed a contempt for democracy.
And, as I said, if Trump seriously believed it then what happens if he wins? But, of course, in that eventuality, all complaints over the legitimacy of the protest will magically disappear on his side.
When you are saying that either the election is free and fair, or your opponent wins, then you are saying that you have no respect for the process. And you are telling your supporters the same. In the days that follow a Clinton victory, I should not be surprised if Trump back-pedalled fast, accepting the result as graciously as possible. The thing is, though, it will be too late by then. He has already told his supporters to "monitor" the election process (which is stretching the boundaries of law, anyway). Good luck telling those die-hard Trump supporters, who believe his "we are going to win!" rhetoric so passionately, and hate Clinton so much, that they cannot see that Clinton might also win legitimately -- good luck, telling these people that it's all fine now and they can accept that the election was free and fair after all, after weeks of believing that it was not. It only takes a few of these to screw things up for everyone, whatever that ends up meaning in practice.
It's a very dangerous message. In his desperation either to win, or -- more likely now -- to try and save face if he loses, Trump has flirted with all sorts of ideas he should never have countenanced. If he wins, well, we had better hope that he was just kidding with us all along and that he's actually a serious guy capable of demonstrating hitherto-unseen levels of calm and restraint. But even if he loses, the story still won't end here.