Anyhow, sure, if you want to give away your freedom to actually own your devices, just so you don't get spam... I guess that's your choice. I just don't want to be locked into a system where that's the only choice.
Regardless, iPhones also receive SMSes. If it's impossible to spam over iMessage, they'll just use SMS. If it becomes impossible to spam over SMS, then presumably Apple can implement similar measures for iMessage that don't require us all to have hermetically-sealed, locked-down devices.