They are fringe, yes.  The lead-crime hypothesis may eventually come to be accepted, but it <i>isn&#x27;t</i> currently, and outside of the laymen pushing it, it doesn&#x27;t have much traction.  It&#x27;s not enough to note lead&#x27;s toxicity and thus, <i>bang</i>, a massive sociological trend is explained.<p>Yes, lead <i>might</i> be a contributing factor in the Boomer crime wave - it might be proven, one day.  But the laymen pushing the hypothesis start out with <i>this is THE explanation!</i> and then retreat to <i>you can&#x27;t PROVE it doesn&#x27;t have an effect!</i>.   This is classic behavior by supporters of psuedo-science.