It's not an Overton Window problem so much as a federal law problem; state decriminalization is easy and low legal risk even when it conflocts with federal law, state tight regulation is more problematic, since compliance produces evidence for federal criminal prosecution. With marijuana, there has been federal tolerance of state liberalization which somewhat mitigates that concern, but that seems less likely with mushrooms.

The Overton Window encourages factions to push extreme positions to move the middle ground of what is acceptable, but still it is the middle ground that is acceptable, not extreme positions with an excluded middle.