So what if they do erect this "virtual wall"? People will just access those sites through some non-EU based proxy. Unless they block access to each and every non-EU based proxy, of course.
Where would you put your proxy to be clear of both "think of the rights holders" and "think of the children" as valid reasons to filter your access ?
So, what you're saying is that EU countries would block access to the proxies in other countries because of these reasons that you mention? Possibly. They might try to do that, but I'm not sure that they would succeed. There are too many proxies, and new ones pop up practically ever day. Unless they block access to any non-EU server, in which case EU becomes North Korea.
Oh, it's probably not about making it impossible. Just about inconvenience. The Chinese firewall can also be easily circumvented.
Of course you are right that it will be a leaky wall due to the nature of the Internet. But it will increase the cost and hassle and reduce bandwidth. And that is good enough to prop up publishing industry revenue.