Beitzah 9b seems to undermine a famous Tosafoth in Shabbath 95a that introduces a fascinating Hiddush that Boneh (construction) on Yom Tov should be Mutar, but is forbidden because of rabbinic enactment due to its mundane nature.
Beitzah 9b has R' Yehudah reconciling B' Hillel and B' Shammai to agree that it's Asur to carry your roof-repair ladder to do something Mutar on Yom Tov because of Marith 'Ayin*.
If that is the case, then how could Tosafoth come up with the Hiddush in Shabbath 95a? Isn't it undermined by a plain reading of the Gemara in Beitzah?
*Though it seems to be widely held now, the idea of applying Marith 'Ayin to Isurei DeRabanan is not at all clear, and it appears as a point of direct Mahloketh between the Sha"Ch and RaM"A in Y"D 87.