I am unconvinced that this is actually sensible. If Trump actually came out and said "I actually want to kill everybody in Kentucky," do you think the Kentucky state government would be evenhanded in planning the election process? Do you think they should be? If your argument is yes then I think we're actually back to whether democracy is good in itself or because it promotes liberal values. I don't see any particular value in having an open-handed debate on whether I should be killed.
Obviously Bernie was not quite so dramatic but he did more or less explicitly suggest he would remove most of the people and much of the structure of the DNC. That's what being anti-establishment means.
I think it's probably important whether what the candidate is after is an atrocity. Like, sure, I agree that Kentucky should do what it can and then secede if the election goes the wrong way in the face of a candidate promising to kill everyone in Kentucky. But not if all the candidate wants to do is fire a bunch of government employees. The IRS shouldn't be shaking down donors to a candidate that promises to radically simplify the tax code and fire the IRS. The police shouldn't be declaring that polling places in places likely to go for Clinton are in danger of violent protest and so everyone who wants to vote there has to be strip searched, even though Clinton is much more sympathetic to police reform than Trump is. I definitely don't think that what Sanders wanted to do would have been so much worse than what Clinton will do that it justifies scorched-earth opposition. So
if the DNC is obliged to be impartial in something like the way the federal government is, then "playing favorites" would be a big problem even though Sanders wants to do things to the DNC that the DNC doesn't want done.
Wait, you're conflating a bunch of things here. I'm responding to the question of what "fairness" is, not what the goal of our electoral process is.
Oh, so you're arguing that it's not unfair
to Sanders to advantage Clinton because Clinton is more personally deserving? I think the response goes similarly - the important kind of fairness here is not fairness to candidates but fairness to voters who support candidates. I expect that many Sanders supporters would eventually get here even if it's not where they start out. The idea would be that it is not fair to Sanders' supporters, who are largely members of the Democratic coalition and will vote for the Democratic nominee, etc., to disadvantage their choice just because Clinton is more
personally deserving (obviously they would probably dispute this and say that she's not more personally deserving on account of being super-corrupt).