The people aren’t the only reason, apart from their direct damages. There’s also the fact that rampant viruses literally drain the community they are in, and are a harm to the online community as well.

Few of the people we are talking about understand computers, meaning they need to have someone else deal with it, or continue to be compromised. Banking info being stolen means more work for the fraud department of the bank, and the police, potentially even the FBI if the issue is large enough.

And rampant viruses mean larger botnets, more computation being leeched causing more electricity usage. More online disruptions of services, and more general spam from compromised accounts trying to spread the infection.

As for iOS, yes and no, and a clarification point. Yes, it attempts to force updates through deceptive means to get the users consent to install at some random point “tonight” which cannot be scheduled. You can turn this off, though there are many reports of this being reversed for some unknown reason. They’ve also moved to force installing security patches without consent, even if you disable the auto update.

The clarification point, is that iPhones are some of the most locked down devices out there. Even if you manage to get an infection, the majority of the time it’s only able to work within the normal sandbox. On top of that, iOS is one of the “most updated” OSs out there. Apart from the users trying to preserve versions for jailbreaking and related tools, or devices enrolled in certain enterprise situations, you’d be hard pressed to find someone on an old version even a week after a new release.