General Consistency of the Apostle
Who is this your most audacious asserter of all immodesty, plainly a “most faithful” advocate of the adulterous, and fornicators, and incestuous, in whose honour he has undertaken this cause against the Holy Spirit, so that he recites a false testimony from (the writings of) His apostle? No such indulgence granted Paul, who endeavours to obliterate “necessity of the flesh” wholly from (the list of) even honourable pretexts (for marriage unions). He does grant “indulgence,” I allow—not to adulteries, but to nuptials. He does “spare,” I allow—marriages, not harlotries. He tries to avoid giving pardon even to nature, for fear he may flatter guilt. He is studious to put restraints upon the union which is heir to blessing, for fear that which is heir to curse be excused. This (one possibility) was left him— to purge the flesh from (natural) dregs, for (cleanse it) from (foul) stains he cannot. But this is the usual way with perverse and ignorant heretics; yes, and by this time even with Psychics universally: to arm themselves with the opportune support of some one ambiguous passage, in opposition to the disciplined host of sentences of the entire document.
Source: On Modesty (New Advent)