So the purpose of Roth-Questadt was to try and damage Michael's standing, at least, dent his legitimacy “in the court of public opinion”
l
Yes. From their viewpoint, they couldn't lose. Frankie simply testifying that he "murdered on the orders of Michael Corleone" would have seriously damaged Michael's legitimacy in front of "millions of [his] fellow Americans," whether or not Michael denied the charges, or "taken the Fifth." It was almost foolproof--except that they hadn't figured that Fredo would tip Michael to Questadt belonging to Roth--and Michael bringing Vincenzo to the hearing.
