Bishop Fellay laughed and smiled (see the screenshot above), as he described how he and his high school classmates “invented the texts for the [new] mass” which was offered at the conciliar school he attended. Here is the full 2009 interview (including Bishop Fellay’s laughter, beginning at about minute five): https://www.youtube.com/watch?v=4XhhM8WXjFA
Such liturgical experimentation is a sacrilege because it fits the definition of “sacrilege”: viz., it is the “irreverent treatment of the sacred”. Summa, IIa IIae, Q.99, a.1. Further, sacrilege is worse than abortion, because sacrilege is a grave sin directly against God, whereas murder is a grave sin directed against man. Summa, IIa IIae, Q.99, a.2, sed contra; IIa IIae, Q.13, a.3, ad 1.
We presume that Bishop Fellay would not laugh and smile if (hypothetically) he were telling people how he used to perform abortions. The fact that he laughs and smiles while telling people how he used to commit the much graver sin of sacrilege, shows how little he understands (or how callous he is) about committing these sacrileges.