The Gemara tells us that ‘Beis Nitza’ were conscientious people and the gezeira (of dragging a heavy bench on a stone floor) did not apply to them.  Asks Rav Moshe Feinstein, we don’t seem to find that the Chachamim would differentiate between people when applying a gezeira; if so how were Beis Nitza allowed to exempt themselves from a universal gezeira?

(Although we learned earlier about exemptions for Kohanim in the Beis Hamikdash, or by the Korban Pesach, that is because the gezeira was never meant to apply to those scenarios in the first place)