My takeaway is that Superhuman is a scuzzy company that I want nothing to do with, but my takeaway is also that Superhuman backing down doesn't really solve the problem. Everybody does this -- and I don't care if Superhuman is worse than everyone else, none of it is acceptable.
An immediate partial solution is for us to push very hard for email providers not to load remote images by default, and (better) for image providers to load remote images one-by-one, rather than in a single batch (which would make it less likely that a user will accidentally turn the tracking pixel on with a single click). An email provider loading images by default should be derided the same way that loading a blog post over HTTP currently is. Have good defaults that protect your users. There should be a swath of email providers on Twitter right now reassuring their customers that tracking pixels won't get loaded by default in their clients.
If you're upset about this, I don't want you to be less upset. But I want you to think about being also upset about stuff like Amp for email, which will make it even easier for companies to pull this crap. I want you to also be upset about email providers that don't turn off images by default, or that don't do any background caching to obscure IP addresses.
There's a large number of obvious improvements to make in this area, and a lot of discussion to be had about non-obvious improvements. If people are only mad at Superhuman, then the overall machine will continue as normal, and all that anger won't actually accomplish much in the long term.
Superhuman is calling this a critical feature, so they're not getting rid of read receipts. My perspective is that their business model is built on a technology that shouldn't work. They're speculating whether there could possibly be a technology to support consent. I couldn't care less about theoretical consent technologies, I want their entire business model to stop existing.