If you're talking about the wake...Michael was not in the room so therefore Tom would have no need to 'please' him by virtually brushing Fredo off with the 'In the boathouse - waiting for you to leave.', and then, 'Not a chance...' replies. It's doubtful that Mike would care how Fredo was kept away from him, as long as he was kept away.

I think that as an actor, Duvall made the choice to display a kind of disdain for Fredo, due to what his actions had nearly cost the Family. Had there been any iota of 'brotherly love' or affection, his reply might've been just a bit more sympathetic. I think this is all very clear, Fredo was a virtual outcast to all but Connie.

But again to respond to the ORIGINAL question...Tom may have been horrified by Michael's decision to kill Fredo, but as a lawyer may have felt it was justified (which it was).

Apple