Sarkozy's government introduced a proposal to criminalise repeated visits to sites that gloried terrorism. Since coming to power, the Socialists have tried to kill this measure off but the UMP, of which Nathalie Kosciusko-Morizet is a member, are still pursuing it. She spoke in the debate on the subject, saying that one "of [her] employees in the town council [Longjumeau (Esssonne)]", has been "married for twenty years to a man which engaged in a process of radicalisation":
She has four sons, among which the two eldest, engaged in the same process, are openly under surveillance; as for the third, he is 15 and is subject to the same influences as his brothers, who live with the father and give him the addresses of internet sites that show scenes of decapitation, done by men with large black swords, with repetitive music in the background.Source: Rue89
It visits the same sites habitually and repeatedly. You could always say that it is better to put him under surveillance in case he does any more than that, but that fact is that today he is in danger, and nothing can be done about it.
Your arguments apply above all to young people about 20 years old engaged in a process of radicalisation; but these decapitation videos are being passed around in school classes.
Note she says that it is the 15-year-old in danger, but in truth it is the French people who have been endangered by the presence of these jihadist aliens on their soil. She says there is nothing that can be done about it, but would a French government hesitate to take children away from a militant "far-right" activist in the same circumstances?