I will not speak for the legality of auto-renewal, as this is something that has been vastly covered. Whether the law is established by court decisions or by legislation, what is clear is that a business IS ALLOWED to incorporate auto-renewal into their membership services, provided they have made this clear in their Terms & Conditions. What I will however speak about is the occasional misuse of this practice.
The auto-renewal option is offered as a matter of convenience to the consumer. A consumer does not have to be inconvenienced by having to go to a website and manually pay for an extension of his/her membership. What pushes this practice into the realm of predatory is when a business patently uses this service as a means to coerce a consumer into payment. In my case with InterNations, it was a refusal to refund my membership within a 2 day time frame of my negligence to cancel on time. What has been originally intended as a tool for consumer convenience has been flipped around into an opportunity for profit (with no future services that will be rendered, as I do not use the Albatross service, I may add). Further evidence of such malevolence, typically auto-renewal comes with an email warning just prior to payment. In this case, no heads up whatsoever.
What is clear is that, although mostly permit-able by law, businesses that take part in these practices must be exposed under our protection of free speech.
Perhaps you have some interesting ideas as to how consumers can use open free speech as a means of recourse against unethical business practices!