A persistently visible ad for a paid service you don't want, in a paid product you paid for? That alone is a justifiable reason for the outrage.
But the more important bit is that, if legal says "no", then "but it's inert" isn't an answer people are willing to risk their employment for.
Also:
> if it turns out it’s phoning home with training data by default then I will also change my tune, but it doesn’t seem to be doing that
We live in the age where open source package managers and build tools come with built-in, opt-out invasive telemetry, and I'm talking bona fide OSS, not something by Microsoft. It's reasonable to assume that the plugin is, or at some point will be, phoning home, until proven otherwise.