It seems to me that Bitcoin maximalism has grown into a cultish group of individuals who tolerate nothing but Bitcoin. If it's simply Bitcoin over shitcoins, that would be acceptable. But it seems the movement has moved to the farthest extreme so that intolerance has grown toxic rather than helpful. We seem to have observed intolerance against innovation in general, intolerance against all other forms of investment, and so on.

The movement is now seemingly characterized with closed-mindedness rather than encouraging constant exploration and innovation and finding ways and possibilities to improve things, which was precisely what Satoshi did.

Other than this, it seems some who have been loudly claiming to be Bitcoin maximalists showed double standard. And some have eventually given up that label not because of realizations but because of financial prospects.

It can be "Bitcoin maximalists", "crypto bros" or "NFT bros".
There's always a group delusional fanatic supporters, who think that the object of their worship is the best invention since bread.
If claiming that Bitcoin is better than shitcoins makes me a Bitcoin maximalist, then I am a Bitcoin maximalist. It's true that Bitcoin is better than the shitcoins. However, I wouldn't mind an altcoin that is actually better than Bitcoin. Unfortunately such altcoin doesn't exist.
I definitely don't think that Bitcoin Core is perfect and I don't believe that Bitcoin will become the one and only global currency.
The Bitcoin maximalists tend to believe in such statements. Maybe I'm not a true 100% Bitcoin maximalist after all.

Maximalism is harmful in any sector and majority of the time it doesn't make sense! As a real world bitcoin user, we need to be practical more than anything. Then only we will be able to put our best foot forward. Maximalism will force you to go all out even when your arguments have stopped making sense!

So I don't think a sane person would ever become a maximalist in any way. Rather they will try to avoid those people at any cost!

Just read the article. The definition of a "Maximalist" in it is broad enough to include people like me, who don't oppose altcoins generally, but do oppose some of the "traits" in the altcoin space. In my case, I'm particularly concerned about crypto projects which hide their centralist nature from the public, in my opinion mostly to be able to "ride the Bitcoin train" without getting control (and profit in an old-style, centralized way) out of their hands. (Thus the "decentralization maximalist" phrase below my boring avatar). But I have no problems with altcoins with Bitcoin-style openness like Monero, Groestlcoin or Grin, for example.

Generally, the Forbes article puts the focus more in the open, decentralized nature of Bitcoin (and Proof of Work as it's "base technology"), and not so much in the opposition to other cryptocurrencies. So I can agree with most of the statements of the "definition". The only point where I disagree slightly (so I'm maybe not a "true" Bitcoin maximalist) is the ignorance of the issues regarding energy sources powering mining and its carbon footprint. While the protocol for sure doesn't discriminate between miners working with fossil energy and those using renewables, the community itself should be able to promote the second group. The stance of some Maximalists that it doesn't matter which energy is used can be seen as a symptom for a trope I see critical in the Bitcoin community: to ignore the social aspects of the Bitcoin protocol. Code may be law in the Bitcoin protocol but there may be other "rules" (or perhaps "guidelines", as they can't be "enforced" easily) supporting it - like a commitment of the community to try to reduce the carbon footprint.

Huh. Still better than Altcoin tribalists.

Answer me this: We have an idea. We can write code to implement that idea. It's something bitcoin isn't currently capable of doing due to consensus limit, and would require a hard fork (e.g., turing completeness, ring signatures, block size increase). But, what you'll be working on, is still money. So, you have two options; make that currency backed-by based-on bitcoin or don't.

Can you justify why you'd choose the latter over the former? It appears to me that crypto coins are scarce, but cryptocurrencies abundant, which nullifies the whole money concept.

The bitcoin maximalists I know are more about individual beliefs about crypto most importantly, this represents someone's thoughts in reviewing bitcoin in the past and present, because they believe bitcoin can have a positive impact on society, with various assumptions and reviews, but more specifically I cannot explain what is meant by maximalism.
If you open your eyes, maybe this Maximalist has a strong meaning for individual thinking in the valuation of bitcoin as the most important.

I implied that every cryptocurrency gives solution to the same problem, that is double-spending, other features asides.

Or you can implement it now, but instead of new currency, you can utilize the already existent. Do you want to add smart contracts that can't be implemented on Bitcoin blockchain? Make a sidechain (e.g., rsk). Your rules, but not your currency. The foundations of bitcoin are invaluable. Part of the ingenious technology is the stable, scheduled, human-resistant monetary policy.

So point me to merchants that accept more than 10, 20, 50.

Isn't that just being a Bitcoiner though, and not a maximalist?

To be fair with other cryptocurrencies, 99.9% aren't even trying to fight bitcoin in the currency category for a while now; a huge majority of them are trying to be pseudo-equity of a platform. Like stocks, but freely accessible to almost anyone.

Want to agree but the loudest ones I used to come into contact with weren't even total nutjobs but were even just chest-out mealy-mouthed business suits who got lucky with Bitcoin, secretly invested in alts, publicly invest more in Bitcoin but ask them to sign a transaction and they'll fumble to figure out if they can do that with Coinbase Pro and Limited Edition gold-plated Ledger (I made this one up but not surprised if it exists). Not sure if they even really ever used Bitcoin in a supportive way.

Super toxic, pay to be seen at events and conferences... you know who they are before you know who the vegans are.

I do actually like most maximalists, they appear so to me, perhaps have never claimed to being one themselves.

It is funny to know that the term "bitcoin maximalist" was first introduced by shitcoiners who couldn't argue against those who were simply pointing out the flaws in the shitcoins they were bag holding. For example if you tell a ETH bag holder that their shitcoin is centralized with a mutable blockchain, they would reply by calling you a "maximalist".

Otherwise any bitcoin, specially those who are interested in the Bitcoin technology (not just profit making) are actually very keen on any other development in alternative cryptocurrencies. It's just that we are too tired of seeing the same copycoins claiming they are "better" just because they did something silly like changed block interval from 10 minutes to 2.5 minutes

I disagree. They are benefiting from two things:
1. Bitcoin history.
They basically tell newbies about how bitcoin has gone from $0.001 to $70,000.00 and convince them that their shitcoin can do to just because it is worth $0.000000001 today.

2. People's lack of technical knowledge
They rely on the fact that when you tell people a particular shitcoin's blockchain is mutable and centralized, they don't understand what it means and why it is bad.
They also rely on being able to convince them that the meaningless change they introduced in their  copy of bitcoin "solved" a "problem".