I'm going to be even more controversial and contend that neither historical context nor primary sources should ever be necessary to legitimately criticise an idea. Primary sources and historical context are certainly valuable for the study of history and culture—but any idea worth its salt should always be able to stand on its own. By way of example, one shouldn't need to have studied the Rigveda, or understand the historical context of ancient India, in order to have reasonable ground as a proponent or critic of modern yoga practice.

Being belligerently uninformed sounds super persuasive, for sure

I certainly wasn't offering advice about how to be persuasive in marketing your ideas, or criticising ideas. That's an entirely different kettle of fish.

If being able to quote from the Rigveda is important to changing your mind about whether yoga has positive physical effects on the human body, then I suppose anyone motivated to convince you should probably do that.

Even secondary sources would suffice here.