It can be anonymous for new users of porn.
As already mentioned in this thread many times, porn users can't remain anonymous. You have to show that you are above the age of 18, to get subscription to these websites. If you are using an anonymous payment option such as Bitcoin, you might need to give some other identification, such as your social security number.
I am sure this can one of the reasons why these websites do not accept bitcoin yet. they have to obey the law and if they use bitcoin, there might be minors registering in their website which is illegal.