letting right wingers in allows the DNC to go "look, we accept criticism from the other side" because they recognize that Democrats already disagree with everything they're gonna say about the speeches whereas someone like Liz, Brace or Hasan might make certain criticisms of the party that they don't want getting out because some liberals/progressives and independents may take them seriously. They also want right wing attacks against them bc that's the way they're moving anyway so it's a form of confirmation bias.

The Democrats absolutely do not want any leftist criticisms of their party being platformed at the DNC, even on an independent stream.