Hi Robert - I'm struggling a bit with your terminology asking how the automation can be turned off. Automation isn't a switch in Marketo, automation is Marketo. The only way to turn off automation is to log off the application. Everything is automation.
In your specific example, you want help with the Unsubcribe logic.
You have a page, on which is a form, with only the field email address visible. But on that form is also a hidden field, Unsubcribed which should be set to the value of true. When someone confirms their email address, the form itself automatically passes the value of unsubscribed=true to the database, and the person is unsubscribed. That's the easiest way.
You could also write a smart campaign, when the form, unsubcribed is filled out, then unsubscribed=true. But I think that's sloppier.
Does that perhaps help? Nothing is turned off. You just might be missing the hidden field.