Did Frankie & Roth have to be killed?

?
Yes or no? Please give your reasons.

Yes they did. Frankie was going to betray lcn especially Michael. Roth tried to have Michael whacked. Pretty cut and dry in my opinion. But what crime did Frankie commit that was so horrible his only option was to testify? They tried to murder him and hes in all sorts of trouble? How exactly did Fredo set up Michael?

Yes. In his own brain, Michael couldn't justify killing Fredo unless Fredo was placed into a dehumanized "enemies" category who all had to be eliminated. Michale couldn't kill Fredo unless he killed Roth and Frankie, too, and Michael was going to kill Fredo.

Technically, Frankie wasn't killed. He took himself out with Tom's convincing him his family would be taken care of. However, I'm not sure that was even necessary. He was in jail and was a known perjurer. The government couldn't afford to believe anything that came out of his mouth at that point. He could have been left to rot in jail for the rest of his life.

IMO, they both had to die for two reasons:

First, they were too dangerous to live. Although Pentangeli's credibility as a witness against Michael was nil after his Senate recantation, the government wasn't going to let him "live better than most people on the outside" with no further ado. They'd keep hammering him for info on Michael (and he had plenty) until they got something they could use, and that they could connect to a witness they could squeeze who wasn't compromised like Frankie. Roth was Michael's most potent enemy. Despite having a near-fatal stroke, and almost being killed by the bodyguard, he still managed to ensnare Michael in a perjury trap, and almost succeeded. He'd never stop until he stopped breathing.

Second, Michael had to prove to enemies, potential enemies=--and those around him whose loyalty might waver--that he never, ever gave someone who crossed him a pass. And, it didn't matter if he was on an Air Force base under 24-hour guard, or if he was being arrested by the FBI--or if he was Michael's brother--they were going to die.