Sure thing Turnbull “If they settled, one more worry off of his mind”
However “If they killed Pentangeli, more proof of Roth's duplicity” - My take Michael didn't need “any more proof of Roth's duplicity”

Also Pentangeli was too valuable to Michael and not expendable as Michael needed Pentangeli as his muscle

Did they have to die?
Originally Posted by Lana
I believe Michael was not expecting Frankie to come to any harm other than the humiliating back down, perhaps handing over the three territories and in the process looking weak etc.

In my opinion if Frankie is killed and Rosato brothers, Roth's ally take over the Corleone operations then Michael loses his muscle and becomes just another casino operator, easy pickings for anyone which would be bigger worry for Michael?

As you have said [or similar!] many times, Turnbull, when blinded by revenge and greed it can affect the judgements of even a master manipulator like Michael

“Michael never more reprehensible than in those two scenes”
Michael hugging Fredo at Mama's funeral and then Michael's chilling kill order look at Neri perhaps could take the top reprehensible scene?