Let's put it this way: I am largely on board with your line of reasoning, in so much that you're forcing people to make up their mind on what they're really upset about and what the root problems are. :-)

For myself and my own grievances, I'm not a fan of comm protocols that don't allow an open market of clients and servers to exist and to interoperate. I much prefer using the ones that do, and so I do a lot of my group chatting on Matrix in the social spaces where I can. The "green bubble effect" and who gets to control it adds another to my list of reasons to want the more open systems to be well-made and prosper, although it's not a primary driver.

I think you have a nice intentionally harmless approach to this, but I'm still not sure how iMessage is exclusive of other protocols rather than conveniently saving the users from cell providers' charges for SMS and MMS when possible. iMessage still supports SMS and MMS, and it only prioritizes its iMessage protocol when messaging other Apple device users. I don't use iMessage and never have, but my understanding is it communicates to Android users, other smartphones and even dumbphones though the cell providers' SMS and MMS services. Seems like the only ones that should have any complaint here are cell providers for being undermined and cut out of their instant messaging revenues.

My take here is that if iMessage is truly a Better Tool, I'd be great if it was available on any computer that fulfills the hardware requirements to participate. For example, Apple could release an iMessage app for Android (and if they priced it fairly, this would still be cheaper than an iPhone, yet still turn them a profit). Or release specs so others can do so.

Do I think they should be or should feel obligated to do so? I'm not sure. I think society is having a debate about whether modern communication networks have "public infrastructure"-type characteristics and need to be regulated more in general, and this is probably also a question on that spectrum to a degree. Let's say I wouldn't be surprised if one day we come to the conclusion that the answer is yes and a larger functionality scope for what is considered basic interoperability is important to us, but there are also some good arguments against it.

Another angle to approach it from is the spectrum of arguments pro and con of bundling/unbundling of hardware and software/services (i.e. need-iPhone-to-iMessage). Governments which run environmental certification/badging schemes for example are increasingly expanding them to apply to software and considering or enacting rules that are decidedly against bundling with HW. The reason is that it tends to cause more frequent hardware replacements to stay compatible with SW/services and therefore a larger energy/carbon footprint - unbundling allows legacy HW to keep going longer on average. A project along these lines I was tangentially involved with myself was the research to expand Germany's "Blauer Engel" label to software.

What guides my thinking here is a bit overboard and flowery again, and also personal. As a software engineer and teenager myself I cut my teeth on making and maintaining one of the better-known IRC clients at the time; this was my first project that really had other users project part of their lives into it, hours at a time. For me it was quite powerful when I realized that I knew people who had met using my chat software and later gotten married and started families. It solidified my view of the engineer as a supportive toolmaker for others to better live their lives and build civilization. The modern day equivalent to the people who conceived of and made the flint tools others would use to start the fires to tell stories around. Comm tools being broadly available and interoperable and their social effects are stuff close to my heart, and stories of folks suffering from lack of access that isn't due to real technical barriers just aren't great, even knowing the complex economics driving the situation.

> if it was available on any computer that fulfills the hardware requirements to participate

Thank you, that's the walled garden perspective I was missing, same as the complaint of those that want to run macOS on non-Mac hw. Usually the walled garden complaints are from the other side of the wall, Apple device users being prevented from installing what they want unless it is already available from AppStore. I didn't consider the other side of that wall.

Yes, sorta. But I think the case of a chat protocol and "Apple should make macOS available for all PCs" are still a bit different.

For example, speaking personally I have no gripe if Apple doesn't want to write an iMessage app for Android, but I think it would be great if the specs and/or APIs were available so that others could write one, even without reaching for one of the regulation-style arguments mentioned above.

Both imply asking Apple to spend effort. With putting macOS on PCs the effort is obvious. But making it possible for others to write an iMessage client also requires effort: For example designing iMessage's technology in such a way that a malicious client can't compromise the system, keeping the protocol relatively stable and sanely versioned, documentation, and so on. With my engineer's hat on, as an opinion, I think this type of effort would contribute to make iMessage better tech as it's in line with the nature of a strong comm protocol, while macOS doesn't benefit as clearly from being on other computers.

The main counter-argument to it is the notion that walled-garden messengers have innovated faster on UX than the standardized ones and then you're back to unresolved quibbles about what's user value and so on. I don't think we've found the one true way to better-tool-to-more-people yet.