Sorry, Cristina, but Fredo knew from the infamous Sollozzo meeting that you NEVER take sides with anyone against the family. He was there. He saw what repercussions that had on the Family. He knew it was dangerous to let anyone outside the family know if he was thinking something that went against the family. Although I don't consider his actions a betrayal, it showed that his stupidity, coupled with his eagerness to please, made him dangerous. After all, Moe Greene slapping Fredo around made the Corleone's lose face. Fredo's actions in Vegas were just another example of how he could be a detriment to the family rather than a plus.