Serial spoofing is, but Apple cracks down on that too: https://www.reddit.com/r/hackintosh/comments/t9p5ff/psa_usin...
It's really not fair to say that the scene was "just fine" up until Beeper went commercial. In those 10-15 years, there were a lot of changes intended to segregate Hackintoshes from Macintoshes.
> There is a difference between commercial exploitation and hobbyist usage
What damages would Apple claim? That people didn't buy iPhones to use their insular and potentially-illegal messaging service? That they abused the same resources that millions of unknowing users exploit for free daily?
It's Apple's call to pull the cord whenever they want, but it's also entirely their decision to keep iMessage a walled garden. It's impossible for you to redirect the vitriol towards Beeper when the only thing they did "wrong" was sell a solution to an Apple-designed problem.