That naively presumes the BLM guy would have consented to a polite debate. He wasn’t there to exchange ideas with the candidate, he was there to cause a ruckus and get thrown out. Even if Cruz invited him on stage, he’d likely have simply screamed rhetoric until the disruption was intolerable. Cruz is a master of rhetoric vs others playing by the same rules; Trump demonstrated an ability to handle warfare (recognize an attack and neutralize it by force immediately).
Cruz did it with a code pink protester. I watched it.