Capitalist YIMBYs oppose McMansions. They're like the central thing we oppose. The whole point of the movement is replacing large-lot-coverage single-family-homes with multifamily. The whole point of YIMBYism is multifamily housing.

Understand: there isn't regulation against large single family homes. You can build a McMansion anywhere you want already. Your analysis makes no sense: nobody needs to organize anything to allow McMansions; they're the regulatory default. But suburban progressives genuinely believe stuff like this! It's a real problem.