I’m sure there are. Rape as a behavior has survived human evolution because it has some degree of genetic success. But that’s really beside the point. It doesn’t tell us whether rape, or child rape, ought to be legal or illegal. But that should not prevent discussion of whether it should be legal or illegal in a college classroom.
A college classroom is not the fourth grade. Professors are not there merely to shovel a curriculum into students’ mouths. Every place in a college or university is and should be open to the intellectual exploration of the entirety of the human experience and thought.
In college classrooms, regardless of the subject of the course, instructors and students do and should feel free to explore any subject when it comes up. Students and instructors both have the propensity to bring up tangential topics, and in a college setting, at least, that should be encouraged.
Now, there is of course a possibility that a professor might indulge his or his students’ digressions off topic to the point that – say, calculus – is neglected. That of course would be a problem. However, the OP doesn’t say that. All the OP says is that the professor said X and asks whether this is a sound argument (it’s not a sound argument, but that’s not interesting enough to hold my attention).
Given that, we as an intellectual foregathering should be more sophisticated than to start questioning mundane details like what class was being taught and wondering whether the professor was himself a paedophile or a consumer of child pornography. It reflects the worst kind of “Won’t someone think of the children!” anti-intellectualist hysteria.
If the OP had said “My calculus professor didn’t teach us calculus because he spent every class session talking about how child pornography should be legal,” then “Did you report him?” and “What a creep” would be appropriate responses. But the OP wasn’t anything like that and did nothing to suggest that, so those responses are not appropriate.