You only open grapes to make wine.
That is, of course...unless they are SOUR grapes.
Yes, Fredo was up to his neck in conspiracy against Michael. Even he admitted that.
No, that doesn't necessarily mean he knew it was going to be 'a hit'.
Even Michael volunteers that 'Roth misled him' in order to beckon him home. That wasn't just to lull Fredo into a sense of false security. They all believed he knew very little, and provided just enough information (whatever that may have been - it's never revealed) to enable the plot to be carried out.
