Ill go as far to say it's not the worst questionable business practice but it is questionable considering its just a sneaky way to keep people paying for something they no longer want, you can argue the fault lies with the customer for not wanting to jump through hoops to cancel or forgetting to or any number of reasons but i can assure you most would agree if it's easy to sign up theres no reasonable excuse to make it any less easy to cancel and we all know the reasons why are selfish.
Ok, looking from the businesses perspective - if there is a service you no longer want, you cancel it and typically you've agreed to the terms of cancellation when you signed up in the first place. The business will want to (rightly so) take this opportunity to qualify the cancellation - why are they cancelling, can we negotiate a better deal, different package etc - this is not possible by offering a 'click to cancel' option.