Apple has always made services primarily for the users of their hardware. They are a hardware company that makes their own software and services. The hardware purchase funds the software development.
Who decides which platforms get support, if it's not the company making and supporting the service? When BBM was popular, I know a lot of people without Blackberries would have liked to use it, but Blackberry didn't offer it, and no one was threatening legal action against them (that I know of). I don't see how this situation is any different.
There are a lot of exclusive services out there, which are locked to specific platforms. Affording legal protection to anyone who hacks their way into a system, and telling the company they can't do anything about it, would create chaos in the tech world. There might be some cool projects, but business models would fall apart, companies would fail, security would be worse than it already is, and I'd question why anyone would try and start something new when they wouldn't be allowed to control it in a way to ensure profitability. Having everything free and open is great, but at some point these services need to be paid for.
The developer of the software supporting those platforms. In this case, Beeper.
I suppose if Apple wants to say certain users are not allowed to access iMessage unless they've bought an iPhone that's fair. (Maybe you could argue its anticompetitive to bundle services together like that, but I won't assert that point here.) But if that's all this was about then I ought to be able to buy an iPhone, import the access token from that into Beeper on my Android, stuff the iPhone in a drawer, and go about my business. The problem is that Apple wants to dictate not only who has access to iMessage servers, but also how they're allowed to access it. And that is unacceptable in my opinion.
"Security" is a poor excuse. If server side software has to rely on trusting the client then it was never secure in the first place. And if client side software wants to "secure" itself against the person who owns it... that's a form of "security" I could do without.
Who decides which platforms get support, if it's not the company making and supporting the service? When BBM was popular, I know a lot of people without Blackberries would have liked to use it, but Blackberry didn't offer it, and no one was threatening legal action against them (that I know of). I don't see how this situation is any different.
There are a lot of exclusive services out there, which are locked to specific platforms. Affording legal protection to anyone who hacks their way into a system, and telling the company they can't do anything about it, would create chaos in the tech world. There might be some cool projects, but business models would fall apart, companies would fail, security would be worse than it already is, and I'd question why anyone would try and start something new when they wouldn't be allowed to control it in a way to ensure profitability. Having everything free and open is great, but at some point these services need to be paid for.