I think you're conflating two different things when it comes to my comment. While I can agree in spirit, and were someone to release a FOSS version of this that did the same thing, I'd go right along with you on the whole "hacker spirit" thing (like the kid who wrote the original exploit and put it up for free on GitHub), but that's not what is happening here. This:

Enabling interoperability in purposely walled gardens for the overall greater good of the Internet?

is not what's happening, this is Beeper just trying to make money basically selling fake ID's so you can get into the club, and the whole "uwu I'm a wittle startup don't hurt me Apple" is just marketing spin for what I have to imagine was the rather insane assumption on the part of Beeper that they thought they found something that was unpatchable, and/or that they could somehow publicly pressure Apple to not sue them out of existence for what is potentially a crime (laws against hacking usually don't give a shit about the method you use to breech a system, just whether that use is authorized which this is clearly not.) Apple has reasonable claim to financial damage as well, since Beeper is using Apple's servers/bandwidth without approval or compensation. Charitably, Beeper might be hoping that this gets the attention of regulators and they'll legislate opening it up, but that ship has sailed in the EU, and the legal argument for doing it in the states is "we don't like green bubbles" so I wouldn't hold my breath, and even then assuming there is a will in the legislature to do this, I have a hard time seeing how Beeper stays funded long enough to see that law pass.

Anyway, I am not saying this because I personally don't want to see iMessage on Android (realistically I'd like the RCS standards body to get their head out of their asses and relegate iMessage and the various Facebook messengers to irrelevance) what I am saying is that Beeper trying to pretend to be a real business is laughable. Like, this is the type of product I would expect to buy in an alternate App Store with bitcoin or something, not something I would expect a real business to release on purpose with all of the fanfare and 100k's of downloads. It's the technical equivalent of putting up a stand in front of Costco advertising that you're going to print and sell fake cards so you can get into Costco, and you're going to do that by plugging your printer setup into Costco's power to do it. oh, and then when Costco cuts off power, you run an extension cord over to a different outlet. Like, you can argue that you think Costco should do away with membership, but we all see what an insane business plan that would be, right?

edit: This is a really good article from the Verge on the whole thing, but I'm afraid it's more nuanced than "Apple BAD!" so ymmv.