[pikachu_is_cool]

> I don't know of a modern chat app that doesn't have [the seen indicator].

I don't use those either. I stick to texting and iMessage.

> The point of using Messenger is that you're not tied to any other portion of Facebook.

You're tied to their ad platform. Whether you view those ads or not are up to you; but you are nonetheless tied to it. They analyze your private conversations with the eventual hope to manipulate you.