It was Michael at his most manipulative:
He scared Frankie with his shouting about "in my bedroom..." etc. Then, after reducing Frankie to rubble, he asks him "to help me take my revenge." Frankie practically passed out with relief. That's when Michael made him put his head in the lion's mouth by asking him to "settle these problems with the Rosatos."

Michael couldn't lose. If Frankie did settle with the Rosatos, it'd be one more worry off Michael's mind. If Frankie were killed, it'd be more proof that Roth was behind the Tahoe attack. Either way, Frankie was expendible.