So, I'm a straight, white, cis-gendered male. I'm also an atheist who grew up religious. My lived experience is probably much closer to yours than your imagined leftist.
And that's important, because what you've presented here is, I hate to say, mainly a product of your imagination. And even if it weren't, it represents at most the farthest extreme of the spectrum.
The left doesn't want you to shrivel up and die. They don't happily dismiss millions of people as "deplorables." And they aren't asking you to forsake your heritage (just that part of it that involved enslaving, raping, and killing other people, which I'm sure you're happy to do anyway).
Capitailsm isn't evil per se. But unfettered capitalism is. https://medium.com/politically-speaking/debunking-the-myth-of-the-market-utopia-c8de0858d4d6
And the Left's problem with capitalism as currently practiced is that it's NOT meritocratic. https://www.washingtonpost.com/news/wonk/wp/2015/03/10/white-high-school-dropouts-are-wealthier-than-black-and-hispanic-college-graduates-can-a-new-policy-tool-fix-that/
If you think basing pay on seniority is demotivating, try basing it on class and race privilege.
Re: positive versus negative rights, stay tuned, as I have an article coming out about this soon. But I'll just say here that positive and negative liberty aren't as easily distinguished as you suggest, and they don't exist in a zero-sum relationship to one another. The "negative" right to be left alone wouldn't be worth much on a desert island, would it? It's only valuable to the extent that it entails freedom of action, and greater public investments, including investments in human capital, expand that field of action dramatically.
The problems you cite in health care and education aren't a function of our inability to find the resources to pay people. We know how to do that. The problem is the failure to treat people with dignity, which is obviously going to be a problem in a society where you can work your ass off and still be one sickness away from bankruptcy. Build a society that reinforces the inherent worth of all individuals and you won't have any trouble finding motivated people to do any job you want done.
As far as where to draw the line, that is what democracy is for.
Re: speech, as a libertarian, you ought to know that owners of private fora can set the boundaries for acceptable discourse. The government, or at least ours, can't censor viewpoints, but Twitter, Facebook, Medium, or any other private entity is merely exercising its own freedom of speech when it refuses to ratify the hate speech of others.
I wrote a several pieces on cancel culture and free speech, but this one is my favorite. Would be interested in hearing your thoughts. https://dustinarand.medium.com/is-cancel-culture-a-threat-to-free-speech-or-a-form-of-it-3a73dec61cc5
As for your last question, I think it shows a certain confusion. Leftists who are criticizing the founders of American democracy aren't criticizing them for founding democracy, but for failing to go far enough, and for adopting and promoting self-seving lies that allowed them to withhold the blessings of liberty from so many of their countrymen for so long. And anyway, I don't think the Right can possibly lecture the Left these days when it comes to respect for democratic institutions. That's laughable.
In conclusion, I'm WAY more concerned about the Right than the Left these days. Read this to see why https://dustinarand.medium.com/why-im-less-afraid-of-the-illiberal-left-than-the-authoritarian-right-a844b2b82abe