I'm for being able to hack your own device to do whatever you like with it, preferably without active resistance from its manufacturer. I'm against anybody who can convince you to open a PDF being able to hack your device to do whatever they like with it.
iOS has enough zero-click exploits that you don't exactly get a choice between the two.
The point the parent commenter is making is that they want Apple to allow people the freedom to intentionally mod the functionality of their device. Not that they literally want single-click PDF exploits to be a thing.