I was going to start a seperate thread on something related to this, but it ties in well here with my opinion that Michael was right to kill Fredo.

More evidence of my long held belief that Fredo was lying to Michael in the boat house about not knowing a hit was planned was this:

Fredo said Johnny Ola told him Michael was being tough on "the
negtiations," and that if Fredo could lend a hand there wouldbe something in it for him on his own.

Think about this....it is nonsense. Fredo is making it up as he is going along. First of all, having been "passed over" Fredo had no clue what "the negotiations" were....at lease not from Michael. Let's say one day out of the blue Fredo suddenly says to Michael, "Say, aren't you being a little hard on the negotiations with Roth in that Cuba deal?" Assuming Michael was a total moron (which he was not) he would have said, "Good point, Fredo, I'll ease up." Then Fredo goes back to Johnny and says "Ok what is in it for me on my own?" Since Roth could not give Fredo anything within the Corleone family it would have to come from without. Would it be a sudden sellout of the Rosato operation with Fredo running it?
Maybe a piece of the casino operations independent of Michael?
I don't think Michael would go along with this. There was never a promise there was "something" in it for Fredo. The promise (on which Roth would have renegged) was if Fredo helped out with the hit (i.e. opened the drapes) there would be EVERYTHING in it for him. The implication was Fredo would be the new Don, and no longer the one who was passed over.
Fredo plotted to have Michael hit. He had to go just like Tessio.