It's simple. Nothing that happens on my device is their data.

Any telemetry that isn't explicitly opt in with zero consequence for not doing so should be the kind of illegal that gets every asset your company owns seized immediately for non-compliance. All user data collection is spyware.

Invasions of privacy are bad per se, even if you don't use them to serve ads

You kidding? That's literally a troijan horse.

Imagine you buy a new showerhead and it came with a hidden camera sending data to the seller. The camera is enabled by default, with toggle hidden and difficult to find.

This is what it is when you enable telemetry by default.

The desktop client logs and sends lists of currently running processes by default, and they also collect usage data (which channels you open, how long for, who you’re interacting with). In the settings, there’s literally an option for “Use data to customize my Discord experience”. And sure, they don’t show ads, but their third-party integrations do. Article with sources

In the end, processing and storing millions of texts, images, videos and files permanently, and hosting all those live voice and video calls, and making updates to the clients, will always cost more than what they get from Nitro and server boosting. Discord isn’t profitable; they have to make the deficit up to shareholders somehow.

The problem is one of trust; there is none.