Being able to debunk such looney claims is very valuable for students so they should develop these skills not be shielded from exposure to them.
I had a guy simply insisting that evolution wasn't real. "Ok", I say, "what about (found some reports demonstrating observable changes in a species over time)?". "Oh, well sure, microevolution is real, but big things can't change, like humans." And around we go again and again. (Same guy believes that we can't actually analyze someone's genome and that people become resistant to antibiotics, not diseases, and 9/11 was an inside job.)
Show them video, show them photographs, bring in first-person witnesses, and they'll find a way to dismiss all of it. Either because they truly believe what they're saying, or, like a current coworker, they're just a contrarian asshole. That doesn't mean we shield people from these views, but we have to, at some point, accept that not all viewpoints are equal, some simply have no merit and aren't worth discussing beyond acknowledging that some people believe them (would you really want to engage with a flat-earth believer? I mean, it was fun once, but that was enough for me).
* Flunk them for not learning or engaging with the material.
* Limit their time in class discussions if they are not engaging constructively.
* Have the administration remove them from the class if they become belligerent.
Of course, the third item is the crucial one. It seems at many universities these days, administrations are taking the side of the customer, er, I mean, student, in every dispute, regardless of the merits.
Whenever I had to deal with contentious issues as a chair of a meeting this is exactly how I proceeded, much to the dismay of the people who wanted to argue all day.
The people who cause the most issues usually take their rebuttal early and then the debate can proceed amongst the more reasonable people.
That isn't something that can be argued against with facts. You can't present evidence to counter this, because they didn't use facts to come to the opinion. As the saying goes, "You can't reason someone out of a position they didn't reason themselves into"
There are a certain class of opinions that we need to be able to dismiss with just a "that is just not worthy of even talking about." While I believe this list of things should be very small, it DOES exist.
Yes it can. In the context of a law class, there's tons of laws which clearly state that rape is a crime, so it clearly does matter. That's just as factually incorrect as saying "Fraud does not matter because suckers aren't important." You can't just say: "_______ isn't important." in a law class.
If I were a history professor and someone tried to bring up Holocaust denial in my class, I'd first explain why it's absurd to try and argue that all that evidence is somehow fake, which then shows that anyone who tries to defend this position either:
1. Has legitimately no idea what they're talking about.
2. Has willfully taken up the agenda of bending the truth to support Nazi-ism.
I wouldn't shout them down though. That's counter-productive.
Oh, and now you want to argue meta-ethics and meta-philosophy :-p?