It's true that this is only possible when you're logged into a computer that is logged into the same Apple Account, but this setup feels eerily similar to the ability by Apple to use your phone remotely.
Are my worries unfounded? I feel that Apple should secure this better or at least explain how this is already secure. Their help pages are very vague on this.
I set mine up to login automatically, because I'm the only one who uses my laptop and I live alone. If other people were in the house or it was a shared system, I would require the login every time.
If people are sharing logins on the Mac, then I can assume they are trusted enough, or they should stop doing that, because too many things are tied to our logins these days.