The accounts weren't "already linked". They shared some metadata. I was asked if I wanted to link them. I responded "no". Multiple times.
Persisting when someone says "no" is at best, disrespect, at worst abuse and, in the right contexts, rape.
Oh, did I mention I'd organized an ad-hoc anti-harassment policy discussion on G+ at the suggestion of Yonatan Zunger? Irony, it's got an enduring entertainment value.
Oddly enough, I was fine with a G+ account, in fact, that's pretty much the only part of Google I'd been using any more. The YouTube account was just to access videos, and I'd pretty much gotten used to purging its history regularly.
The actual harm to me? Pretty little. Both accounts were pseudonymous. For other people, not nearly so little.
And the message on Google's respect for its users and trustworthiness? Loud and clear: nil and nil.