By this argument nothing should ever interoperate with anything else because clearly that's the first step toward destruction.
I'm writing this on Firefox, which interoperates with Chrome and Edge. Oh no! We need to get these browsers operating on incompatible protocols stat, before they all extend and extinguish each other.
In reality, "embrace extend extinguish" is not a law of nature. XMPP is not ActivityPub. They are separate things with separate circumstances. Did you know that XMPP is actually still functional and open and you can download clients and servers that use it to this day? The stories about how Google "destroyed" it have become wildly distorted folklore at this point.
NotTheOnlyGamer