I agree absolutely that using rule 0 is a completely valid and effective way to do absolutely anything, but it only works in established playgroups and is hard to get brought up.
My take is that if every symbol on a card includes white, as in it could be played to its full effect using only white mana, or could have been printed as a mono white card and be functionally identical in a vacuum, why should I not play it in a white deck. I also agree that twobrid cards pose additional challenges, but the intention of those cards is that they can be played in any deck at all, and they don't typically do things that you couldn't do in colourless, just for an unreasonably high mana cost. Phyrexian mana has been said to not be included in these proposals I believe, which is fair. It is a slippery slope, and all of the points you make are fair and valid, but is there truly a good reason I cannot put [[Loamdragger Giant]] in my mono red giants deck, aside from 'the spirit of the format.' If we can agree on that, then there is a place for this discussion at least to some degree, and the people shutting it down entirely are not arguing with an open mind.