And its not simply that he accused some parents of faking their children's deaths. He also specifically instructed his listeners to rise up and "find out the truth". And he did so repeatedly to an audience he knew to be heavily armed, and prone to violent performances of their beliefs. And he did so after being ordered, repeatedly, to stop saying such things, and to retract his statements. But he persisted, arguably because he wanted the revenue he received from having that audience.

Now, most of these parents have dealt with consistent harassment of varying severity revolving around their dead kids for longer than the children have been alive in the first place. Many of these parents never even got the chance to grieve in peace before the harassment, stalking, assault and attempted murder (not sure what else a drive-by-shooting qualifies as) began.

Certainly, if any of these nutters continued to harass the parents after Jones issued a retraction, that's entirely on the nutter. But the thing about our legal definition of slander/libel is that it does take into account what happens when third parties hear and act on the slander/libel. Like, if I accuse somebody of pedophilia, and somebody else, of their own accord, murders the person I accused, the murder is considered in determining what the legal remedies are against me, even as the murderer is on the hook for the murder as such.