Fans are funny, and pretty simple in their thinking. Good = keeper, bad = trade 'em. That's not the it works. First, there are only a handful of players that are untradeable and none of them play for the Celtics. So while fans may like smart and brown, there's nothing contradictory about saying one would trade them for the right return. Obviously the right return is in the eye of the beholder.
As for butler, no issues trading smart for him. Smart is "try hard" guy. For those of you that miss the point, it also means he limited in talent. Those guys, regardless of how hard they try, can be replaced. As for brown, I love the potential. But he is a lot longer away from stardom than many around here seem to think. Nothing close to a guarantee. And even at his peak, I agree that brown may not ever reach butler or George's level.
And no, you can't use the start of brown and butlers career to infer that brown will be better. If that were the case, there would be a whole lot of guys better than butler. Michael carter Williams would be better the butler. Tyreke Evans would be better than butler. Mike Miller would have been better than butler.
So I think brown plus smart for butler is reasonable trade. If anyone said no, it might be the Bulls.