Did Michael really have to tell Fredo off in front of Tom, Neri and Fontane
Yes. Remember that, before Michael told off Fredo, Fredo angrily shouted: "Mike, you don't come to Las Vegas and talk to a man like Moe Green like that!" Fredo had told Michael off in front of Tom, Neri and Fontane.
Oops! I'd forgotten Fredo's outburst You are right Turnbull Michael had to lay down the law and send the message no one gets a pass
Fredo still took sides against the family with Roth though and ended up sleeping with the fishes