This is an emotional argument, based on feelings. There are a multitude of options for letting your voice be known; the Presidency is but one of many avenues through which you can exert your voice. Work on the folks who actually author and negotiate laws, for instance.
Y'know what's asinine? Handing over the judiciary to folks who would see your vision buried for a generation.
Let's play-out a possible scenario, shall we?
Let's say that the temper tantrum throwers get their way here: Hillary loses here in 2016.
Great. The wench was too moderate anyway!
Trump or Cruz is elected instead.
The new President nominates Scalia's replacement, one in the mold of Scalia.
Ginsburg or Breyer are pretty old; odds are that one of them doesn't make it through the first term.
The new President replaces one. The court is now 6-3 conservative.
Anthony Kennedy turns 80 in a few months. He sees his shot at retiring when the new President takes office.
That 6-3 majority gets younger. The chance to flip the court to a liberal lean fades.
It'll be a few decades before the court could ever lean left again.
Then, in 2020, the voters have had enough of President Trump's asshattery - glorious backlash election occurs!
Bernie 2.0 is elected.
He brings with him coattails: a Democratic Congress!
The dream is being realized!
Bernie 2.0 and the new Congress set out immediately to enact their agenda.
The first batch of bills hits Bernie 2.0's desk. He takes out his pen and signs it, to great progressive celebration.
And as soon as the ink dries on Bernie 2.0's signature, the GOP or their corporate buddies file suit in court to stop this legislation from ever taking effect.
Ruling.
Appeal.
Appellate ruling.
Appeal.
SCOTUS, by a vote of 6-3 or 5-4, rules to kill Bernie 2.0's legislative achievement.
Repeat for anything remotely controversial that gets passed Bernie 2.0 and his Congress.
Liberals are horrified to realize: "what good is winning in 2020 and beyond if there's a judiciary in place, ready to kill anything that's challenged before them?"
..
I'm guessing that you consider yourself serious about the long-term viability of Bernie's policy agenda. In which case, I'd say it's foolish to condemn that agenda to judicial death for 20-30 years.
Don't give me a response on how you feel. Or how Hillary is too moderate, or too corporate, or too scheming. None of those responses substantively counter what I've plainly laid-out before you. The mechanics of how our system works don't give a damn about your feelings.
If you're at all serious about keeping Bernie's vision alive for the future, so that we can elect Bernie 2.0 knowing that his agenda is viable, there's only one logical choice in November.