How do you even run a randomised controlled trial of mask usage?

What's the double blinded placebo for a mask?

Assuming you could even get an ethics committee to sign of on the experiment.

I agree the data could be helpful, but I don't think that's the 'right' way to get it.

I agree that it's a simple and plausible intervention. What do you think about gloves, goggles, and tyvek suits?

I'd suggest you to physically make a chart of convenience, likely protection, availability, plausibility, ease of implementation and a few other dimensions for masks and the other instruments you've mentioned. It might help you to see the absurdness of these comparisons.

Those were simple and plausible suggestions, and yet (intentionally) absurd. You invoked costs, benefits, and tradeoffs to make that fact clear. And for what it's worth, gloves still meet the criteria - simple plausible low-cost is not the same as evidence-based. Health authorities (in Canada) most certainly were suggesting we mitigate indirect-contact transmission, with regular sterilization of surfaces using bleach being widely advocated. Gloves are widely available both in their medical and reusable cloth versions, and carry even fewer risks to social disruption than do masks.

I'm totally fine with the structure of the argument with respect to mask mandates as it's typically made. Assuming no costs and at least some benefits, sure, I don't see a problem - this is within basic morality territory so far. But if the parameters are in question? My datapoint: mask mandates have effectively destroyed a familiar relationship, because it put me in the position of asking a good-faith question to a zealot. I judge the costs to me to be extremely, life-changingly high while the benefits remain uncertain.

There's a reason why passenger vehicles don't come equipped with roll cages, 5 point harnesses, and why there's no law mandating that motorists and their passengers wear crash helmets.

Simply put, a 3 point restraint that's much easier to put on provides a decent amount of protection in the event of a crash. On the other hand, if one is engaged in motor sports, racing, etc., then the other safety measures are necessary. Just like one would use additional safety measures when working in a healthcare setting.