I’m not in the business of fixing their mistakes for free.
I will click the unsubscribe link and that’s it.
But there is a (somewhat plausible) defense here: if someone forwards you an email and you hit the unsubscribe link, then it unsubscribes them; not you. Requiring the user to enter their email helps ensure you don't accidentally unsubscribe the wrong person.
That said — the most impactful thing anyone can do to punish dark pattern digital marketing behavior is to report the message as SPAM in your email client. That'll hurt their delivery rates and damage their sending reputation with email providers.
Pre-filling the address in the field is easy and prevents that. But if I get redirected to an empty address field, I immediately close and mark as spam. I refuse to reward that behavior.
They already know your email, I don’t see why getting it again would sell it to a new vendor. Clicking an unsubscribe link already verifies you are a real person.