I would like to create a landing page with one input text box for email address and of course one button to submit the email address.
The user that comes to the landing page is not known beforehand.
Is that possible?
Create a new template based on one of the existing ones, you can do this by navigating to Resources->Templates and make a copy of for instance the Acquisition template.
Open it and go to the properties of the template and choose type generic. Go to Jobs and choose unsubscribe and the service you want to unsubscribe from.
Save the template
Navigate to Marketing activities and create a landing page based on the template you just created.
I am not so sure you can do this with blacklist functionality I did try to set the /context/profile/blackList to 1