I hate social sharing buttons and ad networks just as much as the next guy, so I completely understand where you're coming from with this comment. However, you have the option to completely opt-out of any kind of email tracking by always reading only the text portion of emails sent to you.

Asking whether this is morally/ethically OK is probably not the right question. As we've seen with any technology, if something is possible to track/store/analyze it will be. If tracking email opens (or any data on the internet) is not something we want to accept as a society we need to find ways to ensure tracking those actions under any circumstances is impossible -- not just leave it up to chance.