I strongly suspect that #NeverTrump is not about a principled stand against Trump. Nor do I believe Kristol is sincerely trying to scum up a 'viable third party candidate', or even attempting to simply ensure that Trump is not elected.
I think what we are seeing is a desperate attempt to bring Trump to the bargaining table.
The claim is that Kristol, Romney, Ryan, etc are deeply principled people, who are motivated by staunch Republican virtues to oppose Trump, this loose cannon, this monster. The common rhetoric against them follows that thinking: these guys are so committed to their precious values that they've become zealots! They won't compromise, so they're willing to give the election to Hillary!
I'll be blunt: this looks like a pack of good old-fashioned cocksuckers to me. And cocksuckers aren't motivated by deep commitment to principle.
I suspect instead that this is about something else, something which goes back to the earliest worries of Trump's candidacy: they want to force Trump to the bargaining table. What drives them crazy isn't that Trump is a rotten, terrible, unprincipled, foul-mouthed, whatever candidate. What drives them crazy is that he's in no debt to them. If he can be made to go 'What do you want in exchange for not running third party', that will give them what they want. If he refuses to deal? Well, then they can go to Hillary and ask, 'What will you give us to run third party?' And more and more, Hillary looks like she's going to need that, if she manages to get out of this situation without shackles.
They don't care who deals. They just care that someone deals.