Free speech as understood by modern libertarians isn't the same thing as free speech as understood, implemented, and practiced by the founders. The founders' understanding allowed for restrictions on several fronts, including obscenities, slander/libel, public order, etc.
Individual liberty isn't the same thing as anarchy. Liberty requires you to be mindful and respectful of other members of society, and liberty specifically precludes you from damaging other individuals or society at large with your actions. Nobody has liberty if members of society are free to injure others.
Bork's views on censorship were ordinary and routine until just a few decades ago, til about the 1960's. The founders generally held the same views on obscenities, and there is no contradiction between that and originalist free speech, only a contradiction with the modern libertarian (mis)understanding of free speech.
It's been my observation that libertarians aren't interested in liberty so much as in anarchic "do anything I want any time I want without regard to consequences" total freedom for themselves. They often confuse this sort of freedom for liberty, but they aren't the same thing.
Your gripe with Bork's originalist views on obscenity censorship are illustrative of the difference. The libertarian has a problem with obscenities laws, the originalist/classical liberal/conservative/founders probably doesn't have a problem, at least not in principle.