In the beginning, that debate struck me as being about policy differences - Would Mrs. Clinton's incrementalist approach yield better results if you perceived yourself as being Left of Center, or would the more radical "demand the Sun, Moon and Stars" approach of Senator Sanders? But as the primaries went on, and Mrs. Clinton began to chalk up a delegate lead (especially in the unpledged "super" delegates that the pro-Sanders camp was always suspicious of) the tenor of the debate began to change, and for people on the leftward edge of the party, where most people supported Senator Sanders, Mrs. Clinton went from someone who shared their overall goals, but wasn't committed enough to drive them through Congress, to a wolf in a wool pantsuit, whose motivation for seeking the White House was to enact an intentionally (if not openly) anti-progressive agenda.
For some of these people, the idea that Mrs. Clinton is a deliberate part of "a hateful conspiracy against the masses," as Jack Shafer once put it, and someone more interested in seeing wealthy corporate types retain their ability to expropriate the dwindling wealth of the people is a demonstrable fact, and not simply an article of their political faith. Accordingly, they see a possible Mrs. Clinton administration as an _actively_ Bad Thing, and have no intention of being a party to bringing it about.
To me, it is unjust to describe that in ways that are reminiscent of a child's temper tantrum or to portray it as approval-mining aimed at the like-minded. But perhaps more importantly, it's pointless. Someone who honestly believes that Mrs. Clinton is Evil is not going to swayed by name-calling. You can make the point that, in a situation in which one perceives a series of bad options, that one has an obligation to ensure that the least bad option comes about. But that presumes that everyone bothers to stack-rank bad outcomes. I understand that for some, not distinguishing between undesirables leads to false equivalencies, but in the end all "false equivalency" really means is: "Not finding a distinction between two things important enough to mention or act upon when someone else feels not only that the particular distinction is important, but that a failure to make it can be construed as an attempt to convince others or the self that there is no distinction."
Being something of a dreamer, I've always been of the opinion that positivity is the best motivator. Holding esteem for someone hostage against their obedience only works when someone cares what you think of them. And I'm willing to bet that there are Florida Democrats who still manage to sleep the sleep of the Just, despite the fact that other Democrats are still angry at them for their votes for Ralph Nader back in 2000. (The Democrats who voted for George W. Bush, having been given a pass despite their larger numbers, likely have an even easier time of it.)
For some people, half a loaf is no better than none, and no claims of false equivalency are going to change that. For others, outreach, rather that opprobrium, is likely the best option. An understanding of what it is that disaffected Sanders supporters want, and how Mrs. Clinton's election is the best chance for them to get some of it, is a much better path to gaining their support than preparing to blame them for a failure to bring about the "right" outcome.