When it comes to the purpose of debate, or discussion, about certain controversial topics...I'll put it this way. As a teacher in New York State, there are specific certifications I have to have. One of those, and one that I take seriously, is the DASA certification, known as the Dignity for All Students Act.
This certification means that I am aware of, and capable of, acting on my duty to support the well-being of all students, regardless of their gender identity, race, or political beliefs.
Now, regardless of the fact that I am required by the state to shut down discrimination of any kind targeted at a student of any kind, I would be doing that anyway. It's in my nature.
Let's say a student says that mexicans shouldn't be allowed into the United States because, as Emperor Oompa Loompa might say "They're bringing drugs, they're bringing crime, they're rapists" (sorry, that's not political. Good people don't generalize in ways like that), and I have impressionable young minds in the room that could agree with that, I have a social responsibility to stand up to that. If I don't say anything, if I do nothing, then that effectively means I am allying myself with the beliefs of that misguided person.
On the flip side, if I have a student who says something to the racist, sexist, homophobic effect, as their teacher it is my responsibility to present a conflicting point of view: I cannot tell a student that they're a bad person, that they're a dirty, irredeemable racist/sexist/-phobe. If I am to make my classroom an inclusive space (or a thread) then that means I need to be inclusive and then let my debating skills show, not tell (there's a difference) that their beliefs are misguided.
Imagine if I told an impressionable teen who probably took their political beliefs from their parents (and thus they are normal) that they're the worst and should die in a fire (like some folks online do). That's going to make them feel bad. But then, as often times happens with random folks on the internet, they go back to where they got those thoughts, tell their parents or cohort, and then they come back even worse because now they think you're an asshole for calling them one.
Then there's also the fact that research shows "giving up and calling bigots names" makes the problem worse. If you want society to change for the better, the unfortunate reality is that people won't educate themselves. They need other people to show them the way.
You have to be the change you want to see in the world. If you want the world to be inclusive, you must be inclusive and open-minded.
Even if there is an “invalid” opinion, it needs to be proven, in debate, why it’s invalid. Shown and not just told. Ideally, people would not be the worst and not need to be convinced. But that’s not the world we live in.