Kevin Drum calls this kind of thing "creepy" in his headline, but I think the best way of thinking about it is that it just insults our intelligence and shows utter contempt for voters. Especially Republican voters. And I really don't think it's a Romney campaign thing; I think it's generally a Republican thing. After all, Newt Gingrich. And Michele Bachmann. And Herman Cain.
And the thing that got me going on lazy mendacity was the Scott Walker ACA op-ed that linked to all his cherry-picked examples...and all the context he ripped them out of. To be sure: not every Republican is doing this sort of thing. But it's where the bulk of the active party is.
I do agree with Drum, however, that it's new. He gives a few examples of past Republican nastiness, but he's right: they're different. The Willie Horton attack was at least plausibly true (I don't remember whether the actual ad, produced outside the campaign, was factually accurate or not, but that's sort of the point; what was wrong with that attack wasn't, in fact, anything about whether the story was accurate or not). Similarly, the Swift Boat attacks might have been entirely and totally false, but they weren't obviously false, or easily shown to be false without actually digging up some evidence.
We're not getting this because of Mitt Romney. This is how a party acts when it doesn't care about getting called a pack of liars, on the one hand, and don't care about lying to their supporters, on the other. Romney, at best, is just an excellent fit for the GOP.