A little more context: that article 3 paragraph 2.a. was added by parliament (not proposed by the Commission). But paragraph 1 (same article) was altered to this text:
> Member States shall take the necessary measures to ensure that the intentional conduct referred to in paragraphs 2 to 8 is punishable.
(Emphasis being the change.)
So they only mean the intentional act of putting up pornography without age verification? Just feign forgetfulness, I guess. How is a negative act an intentional one? Or moreover; how do you prove it? I know neglect and gross neglect are things, so I assume they mean if you don't do it after being asked to.
The positive intentional act, I guess, is disseminating the material. Proving intent and various ancillary concepts like knowledge, etc, are the bread and butter of prosecutors, so I don't think the act would be as difficult to enforce as you suggest. Sure, there might be corner cases where you can say "oops I forgot to password protect that Dropbox link" but certainly porn websites that don't do age verification will have a hard time arguing their conduct was not intentional.