If you publish your anti-extremist, pro-democracy newsletter on Substack -- a platform that was funded in large part by Trump-loving VCs and is run by people who have no problem helping right-wing extremists spread and monetize their bile -- you are not just missing the point. You are helping the people you say you oppose.
There are excellent alternatives: Ghost (which I use), Buttondown, Beehiv, WordPress, Medium, et al.
Please use one of those, and walk your talk.