"In other words, there's virtually no way that such a course could be offered meaningfully."
The issue is not with offering it, but with promoting the offering. It is offered, in both organized and informal forms. It's just not advertised to the general public. Generally it works best within a community of potential amateurs who already have a non-dancing reason for associating with each other or at least being aware of each other. For example, such an orientation is one of the most key services that college teams provide to both competitive and social members.
One reason it can work is that there isn't really much conflict between the interests of serious amateur couples, and that of the highly skilled, generally independent professionals who coach them. Business gets handled in a very straightforward manner - good pricing one lesson at a time, discretionary cancellation policies based on respect and trust, etc. While there are regrets and disagreements from time to time, those pros aren't really threatened by amateurs providing guidance to eachother - in fact, they get a large part of their business from referrals arising out of it. Actually, with the majority of advanced amateur competitors now themselves teaching , the difference between pros and serious amateurs is really just a continuous spectrum of degree, from well-informed hobbyist through heavy schedule amateur competitor and perhaps part time teacher, through to full time professional. The real distinction is between those whose role in dancing is primarily focused on the dancing itself, and those whose involvement with dancing is more that of purchasing or providing a consumer product.
Its only where people try to make money off the margins of ballroom - employing semi skilled teachers to spend time with students of marginal commitment, and using a package commitment to try to hold it together long enough to make a profit - that there becomes serious conflict between interests.
Those personally skilled pros who try to own studios with employed teachers can get into some conflict there (usually resolved by viewing the clientele in two tiers - their own competitive couples who are immune to the official business policies, and their employee's students who are subjected to it). But professionals who only do their own teaching and do not try to employ others basically avoid this conflict.
And in many ways, the serious amateurs also establish a two-tiers view - personal friends and potential colleagues get specific advice. The general public isn't refused answers if they ask, but going far out of ones way to vocally pick a fight with people in what is basically an irrelevant business segment isn't wise, unless one is more interested in being a consumer advocate that in personally dancing.
