On the hand I know exactly what you mean about Greenwald and Taibbi (and so many other neoreactionary media folks), but it's also where I get great content from economists (Noah Smith, Claudia Sahm, Doomberg) and technologists (our own Simon Willison, Gergely Orosz, Molly White).
The media folks are clearly escaping scrutiny and playing to their base, but there are many excellent Substackers in other fields!
The media folks are clearly escaping scrutiny and playing to their base, but there are many excellent Substackers in other fields!