Ahh... key word being 'think'. You have no proof, only an (very possibly influenced by others) opinion.
I, on the other hand, have living proof in the form of myself and others who have challenged the "rule". As well as scientific evidence.
By the way, the behemoth forums such as reef central and saltwaterfish.com are a terrible place to get information. A beginner could do no worse than to get his first info from one of them. Their quantity of members is increased, and Callell is right in that they have a higher quantity of members, but the average quality of them is dubious at best.
I think that the 'Tang Police' idea may have been started by human psychology, not the fish themselves. The 'big wigs' got huge tanks to keep a bunch of Tangs in (such as Navarre has himself done; though I have the highest respect for Navarre in all situations but the Tang one), and as they got their wish and eventually had beautiful, thriving tanks (like Navarre's). However, I believe that this is where the Tang Police got their start; since they were very proud of their Tangs (and rightfully so), and some so much so that they wanted no one else to be able to keep them, especially not a casual, undedicated person. The people that had no real desire for tangs caught on quickly to this "noble" idea, and it spread like a virus, eventually outcompeting all other notions and becoming the near religion that it is today.
Think of the "olden days" of "reef" keeping, that is before the Berlin system was brought to America. Aquarists had undergravel filters, coral gravel, and tufa rock to work with. Yet an old book of mine recommends, for a 3' tank, a total stock of almost twenty fish, including two regal tangs. Now if anything our tanks' capacity will have risen, with our deep sand beds, refugiums, powerful protein skimmers, live rock, et cetera. There is no reason to give somebody hell for putting less fish in a larger tank, be they tangs or not, than that reputable author once recommended so long ago. Did she have a lack of knowledge, morals? Somehow, I doubt it; maybe she just was not needing to conform to any made-up "rules", and thus could express the scientific truth.
-Lynden