You dont seem opposed to builds in general, just walking into a game with your build already decided. Is it not prudent to, once you understand what is needed in a game (e.g. DPS, support, pushing, mobility, w/e) have a proven (or at least practiced) strategy for fufilling the role you set for yourself?
For example, How much tweaking are you really doing in game with characters like Erebus where you basically choose to buff your nightwalkers or ignore them? Against heavy AOE teams (Queen, TB, Regulus sometimes), buffing your nightwalkers is probably a lot less effective. Knowing how to play a minimalist (Priests/Erebus) "build" well, having practiced it ahead of time, is probably helpful. Reading how to do that from a more experienced player is not necessarily a bad thing (assuming the guide writer is more experienced which isnt always the case). Conversely, against other teams, nightwalkers can be effective, and knowing how to properly balance these buffs with his other skills and choose the appropriate items can be helpful.
What you are opposed to is thoughtlessness which I agree with. I always lulz when I see people say things like "I am a fire TB player" or "I play ninja rook". Its not builds that are the problem, optimizing a role is useful, its when inexperience governs your build choice that is ruinous. Really the only way to learn what is needed is experience, so new players practicing different builds can be good as long as they dont focus too much in one, and learn the different strengths and weaknesses of them all. That way, once they do have the experience to know whats needed, they got the toolkit to pick from.