Maybe not youthful ignorance, but ignorance just the same. RMS's stance was a libertarian "no harm, no crime"; he reversed it when he learned that there is
inherent harm in sex between an adult and a child.
You may argue "That's common sense, he had no excuse", but RMS is... neurodiverse enough to have trouble with "common sense" in situations like this.
Anyway, his former views are oddly enough broadly consistent with those of the foundational philosophers behind gender theory and third wave feminism, including Judith Butler and Michel Foucault, both of whom believed that pedophiles constituted a socially oppressed sexual class much like gays. Which makes it unsurprising that "social justice" types tend to take glee in exposing and shaming alleged pedophiles (or pedophile sympathizers) from the other side, while closing ranks to defend pedophiles found within their own ranks.