So because you don't think a taboo is important, nobody can believe it's important? Gotcha.
I can't speak for
@Chaosmancer, but I think that just because something is a taboo for some druids, it doesn't make any sense for it to be taboo for
all druids (and by all druids, I mean the base druid class).
It's pretty "taboo"/nonstandard for 5e Wizards to risk going into melee combat and stabbing people with weapons . . . except for Bladesingers.
Undead/necromancy magic are typically taboo for Druids, but that didn't stop the Circle of Spores Druid from going all-in on the spooky theme.
It's taboo for Paladins to focus on necromantic energy, creating/controlling undead, and breaking their oaths . . . except for Oathbreakers.
It's pretty taboo for Warlocks that want good DPR to do anything besides spamming Eldritch Blast . . . expect for Hexblades (and a few other decent options for Pact of the Blade, like the new Undead Patron Warlock).
It's also pretty taboo for Warlocks to be support characters that buff party members . . . except for Celestial Patron Warlocks (and the new Pact of the Talisman option).
It's traditionally pretty taboo for Barbarians to use magic of any sort . . . except for Wild Magic Barbarians, Beast Barbarians, Ancestral Guardians Barbarians, Zealot Barbarians, Totem Warrior Barbarians, and Storm Herald Barbarians. There are more magical barbarian subclasses than nonmagical barbarian subclasses (Berserker and the Battlerager) in 5e now.
These taboos/important character tropes are just that
character tropes. Not "every-member-of-this-class-must-obey-me" tropes. There are no "black and white" class taboos, except for this one strange, nonsensical Sacred Cow that somehow managed to survive its way into 5e. Going against the grain (typical character type) is just as valid of an option as being a stereotypical member of your class. Sure, most druids might have a taboo against wearing metal armor or using metal shields (in which case they should also have a taboo against metal weapons), however, there should be outliers, and the game's "rules" (it's fine if you want to call it that) should not force you to be incapable of going against the grain (by straight-up saying "druids
won't do X". It's fine if there are penalties and trade-offs for doing so, too. Hexblades have to make trade-offs (invocations, attacks, force damage, etc) in order to be different, as do Bladesingers, as do Spores Druids, and every other example in the game.
Taboos should promote character ideas and stories, not be used as a barrier to players that want to play their interesting, non-standard ideas. However, having characters that subvert the taboos/typical tropes doesn't mean that the taboo isn't important, it just means that it isn't a roadblock to creativity for the people that made those characters.