This law was initiated by Belgian members of the parliament, back in 1993 after the Rwanda genocide.
They felt the victims needed a way to defend themselves against those who killed their loved ones.
This was all based in good intentions (recognizing the victims, giving them some hope).
However, the Belgian judiciary system isn't without its weaknesses (like being very late-it takes years for any case); sometimes it is felt the victims have less rights than the culprits.
And now, there's the universal competence law.
However, a few weeks ago, there was a case opened (concerning Gulf war 1, which was recognized by the world community) by Iraqis. Parliamentaries very quickly reacted denouncing the politicized aspect of the law and strongly ammended it in order to let the ministers (executive power) have the possibility to prevent the cases from becoming reality.
Also, a judge might say that the Iraqis could very well prosecute this one or that one in the US itself (paying for a good lawyer, of course), and thus declare its court incompetent.

Raoul