Presumption of innocence is a legal principle and does not and will never apply to a corporation providing you services at their own discretion.
Somewhat ironically, whatever you're proposing would almost certainly require weakening the first amendment. Personally, I'd prefer a strong first amendment (which is concrete and actually means something) to the nebulous "spirit of the 1A".
Do you require a detailed solution before you will even admit there is a problem?
I assume you're referring to the 1A rights of the corporation, e.g. Twitter's right to decline to publish content it disagrees with. I agree with you there. It's a complex problem. My complaint is more with the argument that only the government can restrict free speech. It's a lazy argument because the reality is far more nuanced than that. For example, consider the fact that AT&T doesn't have the right to drop your phone calls when you start talking about Verizon to the person on the other end of the line.
It's totally fair to talk about the "spirit" of the constitution -- that's why we have the Supreme Court in the first place, to interpret the constitution when its words are not clear. I would also note that the Declaration of Independence doesn't mention any self-evident truth about corporations, but it does describe the rights of the people, and government's role in preserving them. If corporations appear to interfere with those inalienable rights, it's not unreasonable for the government to step in to preserve them.
Sometimes platforms ban people I think they shouldn't. We agree on that much. I hope user pressure pushes them into more fair and transparent processes. But I strongly believe they should have the right to publish or not publish whatever they want. And on ideological grounds, I strongly oppose any weakening of the First Amendment.
The extreme social media dynamics somehow holds these corporations accountable for any wrongdoings someone might post on their platforms which is impossible to prevent or moderate in a timely fashion. They respond with more sophisticated and sweeping algorithms that lead to self-censorship by content creators and unexpected actions like shutting down the demoscene event a few days ago.
Further, Twitch is not the entire industry, the same way that Microsoft is not the industry.
The suggestion that it is immoral for a different standard being applied to a private clubhouse is not something that was supported by the influential thinkers who gave us the former idea.
Twitch is hardly in that category, though.
Twitch is not the legal system, but it is passing judgement and renders punishment that can be harsher than the justice system in some cases (losing your main income compared to a small fine). Therefore, it needs presumption of innocence as much as the justice system. I rest my case.