Picking your battles

You could try to see what you can learn from the class. Take the lecturer's arguments seriously, try to translate them from the confused form in which he puts them into the strongest, most plausible version of those arguments that you can create, and see if there are any useful insights in there.

In the quote you gave, you can ignore the nonsense about physics (which isn't really essential to his argument), look past the massive affront to the map/territory distinction in his use of the word "reality," and turn the quote into something like:

When considering the views of different cultures or social groups, students often make judgments about which group is right, which undermines their ability to understand the groups' viewpoints and the processes by which they formed those views. Instead of taking every group's views seriously and looking at the social processes, the goal becomes to explain how their favored group was able to get it right and what is wrong with the other groups who got it wrong. This habit is often problematic even when students' judgment of what social groups got right or wrong is basically correct, and it becomes especially mistaken when they are mistaken about who got it right and are merely aligning themselves with their own cultural group or the dominant culture. In this class we will set aside questions of who is right and wrong in order to avoid these distortions and better understand these processes by which groups develop a framework for viewing the world.

Which sounds pretty reasonable, and similar to what Robin said in his recent podcast about how Democrats misunderstand American politics because they try to explain how Republicans got things wrong instead of trying to understand how these two competing political coalitions arose.

You can still note the problems with his versions of the argument, and with the improved version. For instance, if you set aside right and wrong, it becomes difficult to notice differences between groups in how sensitive they are to external evidence and you're liable to misunderstand social changes which are based on the accumulation of evidence about reality (like the belief in evolution). And it's fine to provide an occasional dose of sanity to class discussions, but you should try to do it tactfully without being a jerk or dominating class time.

You're making a mistake when you take talk of this sort at face value. This is ideological speech, not scientific or technical speech. It doesn't even try to present a rational argument based on facts and logic, and it doesn't strive for an accurate view of reality -- its purpose is not to do anything like that, no more than, say, a love poem has any such goals.

The true meaning of ideological language can be directly expressed only in the language of power. Like any other ideologue, your lecturer has an idea of what the social order and the relations of power should be like, and what measures should be taken to change the present system in this direction. His ideological language is meant to provide a rallying cry for his co-ideologues in order to sort out who is for and who against him, and to strengthen the passion and resolve within his own ranks. Agreeing or disagreeing with it will in practice signal only your ideological allegiance, and nothing at all about your intellectual standards.

If you want to reply to this ideological drivel, then in all likelihood, this is the only thing that your reply can communicate. It is impossible for you to innocently address only its literal meaning, keeping your hands clean from any implied considerations of power -- both the broader social power relations with which the lecturer's ideology is concerned, and the lecturer's own power in his position as an official institutional ideologist. Your reply will be immediately understood as a challenge and attack in terms of power, as a threat that must be met, not as an interesting contribution to truth-seeking. In this sense, challenging ideological language with logic is similar to what would happen if you tried to defend yourself on a show trial.

Whether you want to pick this battle is your call, but be aware that these are the terms in which it is likely to be fought.

I'd be tempted to ask the lecturer to rephrase the whole paragraph tabooing 'reality' - I get the feeling they're not actually saying anything controversial, they're just choosing to use 'reality' in a non-standard way. Of course, maybe I just don't spend enough time with the sort of people who genuinely believe this sort of stuff.

Even in physics we have 'reality' changing as you get closer to the speed of light, and the laws of physics don't apply prior to the big bang.

This isn't even close to being true. 'Reality' doesn't care what equations we use to approximate it.

To answer a question you didn't ask: I'm not sure that raising the sanity waterline is a battle worth picking. Adding water to the sea connotes futility because the sea is so vast; and while it may be that the benefits are correspondingly vast, it seems probable that we can achieve other vast benefits for much less effort, by targeting groups that are especially receptive and especially influential.

Is it worth your time and effort to be the lonely voice of dissent in this class? Does the format facilitate persuading other people in the class? Will you enjoy picking the fight anyway?

Try going meta. Other people must have thought of doing the same battle in the past, since this particular disagreement is not a new one. Imagine how these arguments might have went, given what you know about what generally goes on and has went on in the university. What kind of outcomes do you think there have been, and what have their frequencies been. It's probably easy to imagine a "wasn't worth it" outcome, which involves energy spent on your part, and nothing much changing. What kind of positive outcomes can you imagine?

As for this particular case, I'd figure developing a solid written defense for your stance would be a good academic exercise, regardless of how the battle with the lecturer goes.

Who is the more irrational: the lecturer, who utters the gibberish, or the student, who pays to hear the lecture?

It depends partly on your fellow students. What's your impression of their open-mindedness?

You're bringing back memories of a class I took where I thought the teacher was wrong about a number of things (sorry, details forgotten), and being told a number of times by fellow students that they were there to listen to the teacher and not to me.

I'd say that what you're dealing with is not an emergency, and if you want to oppose those ideas to a large extent (if you want to do disagreement in class now and then, I'm not going to argue with you), post it at a social website where students are likely to see it.