This is Getting Stupid
Really, really, dumb.
Anyone who thinks of themselves as progressive or liberal or lefty in any way but STILL insists that having Trump as President of the United States is a good thing is either lying to themselves, lying to people they're talking to, or has given up on the whole 'thinking' part of what they're saying.
Should she get the nomination (and it looks like she will) Clinton will be running the most left-wing campaign in 40 years. And that, in a large way, is thanks to the successful Sanders campaign. The Democrats in power, the DNC, and all the hidden folks no one sees know what that populism has done for their base. They can, believe it or not, see it on the television just like everyone else does; and they'll be perfectly happy to tap into it.
Note: that's what SUCCESSFUL campaigns do. They draw people to them.
And this leads to perhaps the 'smartest'(?) argument of the Bernie Alone crowd: the idea that somehow the population will suddenly turn to the left after seeing the nightmare that would be a Trump presidency.
It doesn't work that way. Seriously, it just doesn't. It never has, and it never will.
Bill Clinton beat the First Bush by moving right politically, which included compromise policies during his time in office and during his campaigns. He won because the political right was winning, so he moved towards them enough to get the votes he needed to get in power in the first place. The Second Bush won (barely) by... well, I'm pretty sure you know the history.
In short: a Trump win would push the Democrats to the political right, not left. They have to win before they can enact any policies - that's not something to forget. All those 'progressives' who will stay at home? Why the hell would anyone try to get your votes? You stay at home! You don't vote, so you literally don't matter in an election.
As for stupider arguments, those are easy to find, too. I've seen one saying that whoever sits on the Supreme Court is irrelevant, because they die off all the time. To which I say: whay rulings have been delayed because of the current gridlock? Oh, yeah: reproductive rights, voting rights, education funding, freedom from religion in the workplace, immigrant rights...
So, sure, if none of those matter, then you're absolutely correct. Otherwise, you're wrong. But you're probably wealthy enough (hello, Susan Sarandon! You're an idiot!) to remain unaffected in your personal life by any of those decisions. Laws affect the poor in their daily lives far more than they do the rich or middle class.
I've seen another argument saying that it 'won't be that bad' if Trump is president. To which... Dude. Okay, I think he's a better person than Ted Cruz, but only because he's ignorantly evil rather than actively evil.
Otherwise, Trump is a void waiting to be filled by whatever happens to be around him. He is a man with no ideas for running a government. None. He has no policies, he has no priorities, and he never had any intention of winning the nomination, never mind the general election. He will sign whatever piece of paper is thrust in front of him by whoever screams his praises loudest - and when you're in Washington, D.C. that means some professional level bootlickers. He will not care what the policy is so long as he gets his 10:30 AM rimming on schedule.
And that policy is going to be made by people who have no fear of lying to his face. Politically speaking, he is going to be the most easily manipulated president since Warren "Gee-he's-pretty-bet-I-can-make-him-president" Harding.
Internationally? He's got skin so thin they'd be bragging about it in any culinary school. Slices of Trump, hold it up to the light and you can see right through it. Think Putin wouldn't walk big, slow circles around him?
Then there's the argument that Clinton is a Hawk - aggressive on international policy, and prone to war. That's certainly possible, given her stance as Secretary of State. But perhaps you should look up who The Vulcans are, and why they are all Republicans. And if you're concerned about war, perhaps you shouldn't elect the man who throws tamper tantrums when he can't build a golf course in Scotland; or through inaction allow him to get elected.
Just a thought.