Clearly that would be worst possible practices.
I'm subscribed to some mailinglist that I don't actually read but would be upset if they auto-unsubscribed me, because if I'm ever interested, I want it to be there.
It doesn't mention pixels anywhere, though.
It does contain the line:
> "Consider unsubscribing users who don’t read your messages."
But that's only after lots of mention of opt-in and unsubscribe options. And ultimately, you can't really know whether users read your messages or not.
And personally, I still think it's a bad idea to automatically unsubscribe people who are interested in your newsletter merely because they're not loading images. At the very least, make it very explicit that you're going to do this, and maybe give them the option to turn the auto-unsubscribe off.
Using a tracking pixel isn't perfect, but like what peter said in another comment somewhere here, it's the best we've got. If you want to implement Gmail's (and other ISPs) best practices, then you need to do tracking of engagement. Just because you don't like it, does not mean that is not considered best practice. Just because it won't be 100% perfect, does not mean it's not considered best practice.
You may disagree that it should happen, but you cannot factually say it is not a best practice.
You may have had this happen before and probably thought that was just a scammy way to get you to click a link, but in fact it's completely legit.