First of all, they will have a hard time enforcing this, ever, and even if they would succeed in doing this for Belgian sites, it wont stop this from happening on millions of sites around the globe.
They claim to be an independent instance providing a voice for a diversity of people and a place for discussion. Sounds to me that only the opinions they like are allowed, how can you have a discussion if some parties are not allowed to be heard.
If it's not true what they are saying, it should be easy enough to counter any argument the made. If they are correct in their statements, it is of the most importance that they be heard.
This brings us to Fitna, a short movie of about 15 minutes long that cuts and pastes all kind of images, sound bits, newspaper articles and news clips to make some kind of statement. Most of Europe is going nuts over it, though so far nobody has given any good argument against it.
It's funny that, by trying to 'save' us from right wing ideas, they use the same techniques they would not accept from these extremist right political parties.