The money quote is this:
"Ultimately, negative perceptions of candidates could have participation implications by keeping more youth from the polls," they wrote.
What amuses me is that this is supposed to be Stewart's fault. It seems American politics is the only place where the maxim, "If people judge you as x, it's their fault" is considered a universal law. (Kant is spinning in his grave.
(Counter-example to this putative "universal law": if I steal your wallet and you judge me as a bad person for doing so, it's really your fault -- after all, you left your wallet where it could be stolen. While it may be true that you bear some responsibility, it's grievous moral error to think that my fault is thereby eliminated.)