Why is `RUSTC_BOOTSTRAP` so actively discouraged?

MusicalNinjaDad:

the wonderful nightly-beta-stable release process that's in place

Argument from second-order effects: Doesn't it depend on bugs of unstable features being reported from the wild? For that, you'd want people trying out the feature as soon as it appears (which is in the nightly).

Personally speaking, whenever I try to use a QoL feature in my app and see it is unstable, I just switch to nightly to never come back to stable.