> How many windows machines were infected in the early 2000's?
Yeah, that's a very bad analogy, it wasn't about side loading, even assuming that MS was able to vet every application out there, which nobody was technologically or had the resources to or wanted to, the infrastructure wasn't there, the OS security was worse than today and based on different assumptions entirely, the responsibility is still in the hands of the user, and, most of all, with good reason users pushed back on the all TPM/Trusted Computing thing.
So they did not want that feature and voted with their money, until they could not vote anymore, because smartphone ruined it for everyone except Google and Apple.
edit:
besides (obviously) RMS [1] being right and opposing to TC/TPM, this BBC article from 2005 [2] summarizes what even users there were not particularly tech savy thought about the topic
A couple of significant quotes
computing base is also used to make digital rights management systems more secure, this will give content providers a lot more control over what we can do with music, movies and books that we have bought from them
We need to ensure that trusted computing remains under the control of the users and is not used to take away the freedoms we enjoy today
[1] https://www.gnu.org/philosophy/can-you-trust.html
[2] http://news.bbc.co.uk/2/hi/technology/4360793.stm