There are already are and always have been effective counter measures to hazards outside of HDB.
There is no competitive basis to any argument so far seen in the recent pages of this thread against banning boots.
There is no principle of competitiveness that says Volcarona and xyz pokemon that are weak to rocks need to be unoppressed by Stealth Rocks, in fact it is the opposite:
A characteristic of a competitive meta is that players have a reasonable capacity to build a team that covers most of the metagame. As more and more pokemon are introduced, threats proliferate and building a reasonable team becomes more impossible. Moves like hazards which could restrict a vast segment of pokemon, and centralize team construction around moves (which are the basis of competitive outcomes) become more vital than ever to maintaining a playable game.
Your last sentence can be flipped entirely. We do play by effectively 'clicking moves', but pokèmon aren't the only things that are introduced each generation: abilities, moves and items keep growing in numbers as well. Moves are being affected by both abilities and items since Gen 3, all three are basically what Pokémon battling is about. Items have even defined new overarching mechanics in Gen 6 and Gen 7, with Megas and Z-crystals. This is to say, you can't just single out moves being the main basis of competitive outcomes when you choose your movesets with abilities and items (and typings of course) in mind.
With this premise, the way you tackle on HDB has to be reconstructed in a different light: how do you measure its impact on the competitive scene? How restrictive can it be? Does it negatively affect the viability Pokémon, moves, abilities? Does it make entire playstyles more broken? Does it create unhealthy circumstances?
I agree with you that in a vacuum HDB is an absolutely crazy item, top 2 alongside Leftovers for sure. If you try to answer the questions I raised, you'd realise that they are difficult to answer in an objective way. For example, in this generation you use SR a lot to pressure the opposing defensive backbone by forcing passive damage and/or gaining momentum by forcing Defog/Rapid Spin. I've not seen many games where Stealth Rock were just BAD or not worth setting up. You could even argue that limiting the effectiveness of Stealth Rock a bit more is a good thing because of how easy it is to force chip damage with it, considering that it naturally hits everything. You are given the choice to ignore it by sacrificing the item slot or deal with it and use the item slot.
Speaking of this is HDB's drawback (admittedly the only one): you can't use power- or speed-boosting items, leftovers/black sludge or other miscellaneous items like helmet or berries. Many mons that use HDB would love being able to receive passive recovery from Leftovers (mainly defensive mons) or holding Life Orb/Protective Pads/Choice items/Lum Berry/whatever (mainly offensive mons). Chip damage stacks on the generic HDB Pokémon (Regen+HDB is another issue entirely and the broken-ness of it to me is mainly brought by Regenerator), and sources of chip damage aren't only entry hazards: contact-punishing abilities and rocky helmet, sandstorm or hail, burn and poison, damaging trapping moves. Of course, Volcarona and company couldn't have asked for a better item, but that goes to show the power of Stealth Rock as much as the power of HDB.
However, banning a move or an item is incredibly more complex than banning an ability or a Pokèmon, because - as I said earlier - competitive Pokémon is based on MOVES, ITEMS AND ABILITIES and how they interact.
Let's take Cinderace as an example. With Boots, has Cinderace always been broken from the start? No. We had Blaze Cinderace in the tier and it was a perfectly fine Pokèmon. Then again, without Boots, would have Libero Cinderace been broken? Also no. HDB made Ace the ultimate pivot that thanks to Libero+crazy coverage also had pretty phenomenal breaking power. How do you assess this situation? Is HBD the issue, or is it Libero? The answer is: the combination of both. The same logic can be applied to Regenerator mons, ESPECIALLY the Slowtwins which abuse the holy trinity of RegenPort+HDB. This combination is one of the best move-ability-item interactions we have ever seen, but none of the single components individually pushes either Slowtwin over the edge by itself. I would argue HDB is the least valuable of the three, seeing how Slowbro worked perfectly fine with Rocky Helmet, although HDB is definitely still very valuable.
What HDB does can ultimately be divided in two sections:
1) Give viabilty to SR weak Pokémon, mainly defoggers
2) Give even more viability to PIVOTS - the understandable part of the ban-HDB argument.
The first point I can only see as a good thing honestly. The more viable Pokémon we have, the better it is. I understand that for the longest time, keeping stealth rocks up was the way to deal with a certain portion of the metagame, but these pokèmon can also be dealth with outside of rocks. The ones you can't, get banned (kyurem-black, ace), but that's clearly because of their other traits IN CONJUNCTION with the boots, it's never just because of the boots. Secondly, HDB is a gen 8 item and - since we've established how difficult it is to evaluate an item like this outside of subjective frustration - we gotta deal with it: as
Lemingue said, it's the quirk of our generation.
The "principle of competitiveness" you are searching for is simply that this item was created for this purpose: make rocks less punishing. Is it less competitive just because it makes it easier or is it competitive exactly because it gives another layer of counterplay around hazards?
The second point is where it gets tricky, because HDB definitely sinergyzes VERY well with pivots, as hazards have been notoriously their worst enemy and of course the boots negate them as long as they don't get knocked/tricked. it creates longer games exactly because we are used to entry hazards doing a big amount of work against pivots, limiting the amount of switches they can afford. In gen 8 we have developed other ways to defy pivots but they are absolutely living their best lives, especially regen mons, especially the slowtwins that have regenport.
Massive TL;DR.
HDB is definitely a strong item that has defined gen 8 so far. It created a more pivot-centric meta where you can't constantly deal that 6%/12% chip even when rocks are up, and where already good abilities like regen now effectively got boosted. I personally think it's fine right but I can see the issues you guys bring up.