What is so *hostile* for social networks?
I don't know about social networks, but here's why it would really suck for forums. Say you're a prolific poster on a programming forum. You answer, or participate in, a dozen threads a day. Your words are widely quoted throughout threads. These threads are of general benefit to the programming world at large. This forum is indexed by Google, and comes up near the top of the search results for some very common programming terms.
Somebody on the forum thinks you are cool, and uses a quote of something witty you said as their signature line.
Now, one day you wake up with a burr up your ass. You request that the forum destroy all your information. In order to do this, all your posts must be purged. All posts which quote your posts must be purged. All those valuable threads, which went far beyond just you, and developed into valuable information sources for thousands of people, must be purged. All the posts that guy made who had your quote in his signature line must be purged. It's not just YOUR words that have to go, hundreds of other people's posts are affected as well. The usefulness of the forum is at an all time low. People start wondering why the entire forum got deleted. People stop coming to the site. Google ceases indexing it. The forum is dead.
Your post gave me a good laugh.. You obviously aren't from Europe or you have no clue about the laws that already protect your privacy. (But you are good at making funny horror stories)
Here in Europe you can already ask any company for a copy of all data they may have on you and force them to correct it if you find any errors. What companies can do with your data is also severely restricted.
Just so you have some idea about how strict the law for European companies already is, the French CNIL considers a "IP address" to be "personal information".
This "new upcoming EU law" is merely applying current law to companies like Facebook that don't respect even the minimum rules of handling personal data.
Don't worry, the world won't come to an end when the new law comes into effect, we are all civil and reasonable over here.