What does that fight look like, in your mind? Standing and shouting for Bernie and then sitting out the general when Clinton wins? Or arguing for Bernie in the primary since he's the best choice and then arguing just as hard for Clinton in the general since she's the best choice then?
Primary-only voting doesn't force anyone to do anything but ignore us harder in the primary.
And if that isn't what you mean by your objection to framing all elections as choices for "least bad", then why are you echoing the rhetoric of those who do?
So, you are in favor of "my guy or the Nazi" voting? I didn't hear a "no", there.
It isn't "loser talk" to recognize the rules that elections run by, or to push back against the "both sides" rhetoric that lets the Overton window drift ever rightward.
Either you show up and vote in every election for the least bad candidate, be they good or great or only "not as bad", or you are doing more harm than good.