I say let them go, just make sure that they do not return.
More detained in operation against recruitment of Syria fighters

The raids follow on from yesterday’s operation when a score of people were detained in as many raids.
Those detained today are being questioned. A number are expected to appear before an examining magistrate.
Belgian police on Monday launched a massive operation targeting people involved in the recruitment of fighters for the Syrian civil war. Across Belgium twenty premises were raided. A score of people were lifted from their beds and detained.
The operation led by the federal public prosecutor’s office centred on Brussels including the borough of Sint-Jans-Molenbeek, but people suspected of recruiting fighters for Syria elsewhere in the country too were detained. In all ten people were arrested. The others were released on conditions or didn’t have to appear before an examining magistrate after being questioned by police.