Not saying I agree with this line of thinking but I personally think cross platform iMessage would benefit iMessage users privacy significantly. You can't control what OS your friends use.
I think the real reason why might be something along the lines of anti SPAM or botting; iMessage seems to require an authentic, unleaked serial number to connect, as I found out a while ago when connecting my Hackintosh. (I succeeded but I have a feeling many real Mac serial numbers get banned from iCloud by Hackintosh users sniping them out of pictures in eBay listings and whatnot.
I think this jab is unwarranted. Android with security updates is not significantly less secure. Talking historically, Android started with more security measures than iOS, with app sandboxing from the get go. Nowadays modern devices contain dm-verity for verified boot, layered security at various levels including SELinux, etc.
Not suggesting there hasn't been more security issues with Android overall, but there's also more devices and more available source code with Android, and iOS is far from having a clean track record for exploits either. If it did, you wouldn't be so limited in which versions of iOS you could restore in iTunes...
I think the real reason why might be something along the lines of anti SPAM or botting; iMessage seems to require an authentic, unleaked serial number to connect, as I found out a while ago when connecting my Hackintosh. (I succeeded but I have a feeling many real Mac serial numbers get banned from iCloud by Hackintosh users sniping them out of pictures in eBay listings and whatnot.