Well, I think letting people get silently charged monthly without sending them any message about it is a bad idea, even if they say they want it. Similar with not telling them about an outage to their service.
Well, then that mail is going to get legitimately marked as spam when I didn't request it, I have no business relationship with the sender, and there's no other way to make it stop. And the user is still getting silently charged because it's going to my inbox, not theirs.
Unsubscribe is the alternative to the spam button. If you don't provide it, you are asking to be marked as spam, no matter how important you think the email is.
They should have confirmed their user controlled the email address, too, but why not go with both?
And this is hardly confined to Gulf Power. Verizon, Spectrum, countless banks...