When I finally quit my local newspaper, they make it as hard as possible to quit and the customer service rep seemed to want to argue with me before finally relenting. My opinion is that you should be able to quit the same way you joined. If you do it online you should be able to leave online.
My biggest problem with Amazon is not being able to turn off the (@*@#(*@# one-click purchase. I have bought a few Kindle books and had to get a refund with one little clumsy twitch on my phone. Give me an option for traditional purchase of putting into the cart and then buying as a separate action. You can turn off one-click on everything except Kindle ebooks.
I have 1-click purchase disabled. Just for fun I checked. It took less than a minute to find it on my desktop or phone.
Desktop: Account>Ordering and shopping preferences>1-Click settings>disable on all devices
Phone: Menu>1-click settings>disable on all devices