Even on a proper responsive design, sometimes the images are too small to read (like this article for example, which has screenshots of other phones).

Furthermore, even on my desktop I'll use zoom sometimes (you know you can zoom on the desktop too right?) because I can't read something, and it's a lot easier to zoom than to try and screenshot it and then enhance in some other program.

Further down you said you've been on sites where you wish zoom was disabled. Can you show me even a single example? Did you mean that you wish the designer hadn't relied on zoom for their page to work? Because that's a very different thing than "the site was perfectly ok on mobile but they had zoom on and I didn't want it on". In fact, if their design was good enough for zoom to be off, how did you even know they had it on?