I don't know if I know the solution, but I know one thing that
isn't the solution: silencing everyone who disagrees with you.
A lot of the people complaining about "toxicity" on the internet seem to be under the impression that if we "deplatform" the so-called toxic people, that will fix things. But on the contrary, that makes things worse.
If someone says something awful on the internet, and everyone either ignores them or politely presents a counterargument, they either move on because they feel they've been heard, or they engage in a polite discussion. Maybe they change their mind, maybe they don't. If they really can't engage in polite discussion, then they come across as making their ideas look worse, so they aren't really doing much harm.
If someone says something awful on the internet, and everyone rails about how awful it is and gets them banned, then that person is angry, and that anger motivates them to keep posting about it everywhere and spreading their idea. Meanwhile, they will integrate that idea into their identity, which makes it far harder to change their mind. And if you actually manage to get them to go away, they will go to cesspools like Voat, where they are even less likely to be exposed to ideas that change their mind, and where in fact they are likely to be exposed to even worse ideas.
Let's get some perspective: what you're complaining about is people saying things you don't like on the internet. Yes, what they are saying spreads ignorance, but the solution to ignorance isn't silencing the ignorant, it's education.
MLK and Harvey Milk both recognized that the source of the bigotry they fought against was fear borne of ignorance. But the average left-leaning person today doesn't see bigots even as people any more. All it takes nowadays is for someone to say one of a list of banned phrases and they're completely written off as even human. If we're going to bridge the gap here, we on the left have got to consider that we might be the toxic ones.
I've found that when I actually talk to so-called "toxic" people politely, they are willing to listen. It's not them that are causing the polarization.