Marketing email subscriptions you were tricked into signing up for isn't what people consider spam. In fact, Google provides a nice feature to unsubscribe from those without looking for a link in the email.

Now, the spam argument for iMessage makes little sense IMO - you're still going to get the same message via SMS. However, with Apple in charge, there is a chance that there will be some kind of "report + temporal ban" feature. Carriers have no incentive to create such feature.