That's not a bad discussion to have, though! What if showering more than two or three times a week causes your back to break out? What if rinsing every other day is good, but using shampoo/soap/etc that often causes unwanted side effects? What if the optimal frequency of showers for keeping body-odor minimized is every third day, and showering every day or every other day actually makes BO worse? We need data!

(I'm not being sarcastic. However, the optimal showering strategy is likely to vary from person to person, and be influenced by diet, physical activity, genetics, environment, etc.)

like students arguing seriously about how often you really need to shower

If those students live in a society that mostly does not even wash their hands, I'd consider that an improvement.

(Yeah, I'm deliberately misrepresenting your analogy.)

In other words, "like people I regard as low-status arguing seriously about whether assumptions unquestioned by high-status people like me are actually true".

Probably right.

Once a day is the bare minimum for basic decency. Unless you happen to share your water and heating bills with me, in which case more than a couple per week would be the epitome of frivolity. ;-)