Honestly, I think it's silly that people are mocking others for saying yes or for saying no to a teade like this.
I think it's a very close call, and regardless of whether you say yes or no, I think either decision is easily justifiable.
One one hand, people are talking about Simmons as if he has the potential to be a future franchise player - I'm talking Durant / Lebron / Anthony Davis potential.
If he genuinely has the potential to be that good, then it's hard to give that up for a guy like Butler who is a very nice player, but probably not good enough to transform you into a contender on his own.
The way I see it, if you get a guy like Simmons and he has the type of first season that guys like Anthony Davis, Karl Anthony-Towns, Lebron and Durant had - then the future upside will be so obvious that a player of that caliber will immediately improve the likelihood of your team attractive big free agents. If you get a guy like that on a rookie deal for years on end, then you are in a position to easily sign two max contract players to play alongside him, and still have enough cap space left over to build a quality roster of support players around that core. That's NBA team building gold right there.
On the other hand, every rookie (even #1 picks) come with risk. Jabari Parker and Joel Embiid, for example, were considered by most people to be right up there with Andrew Wiggins in terms of their potential to become franchise players. People compared Jabari to Melo, and Embiid to Hakeem. Fast forward a full season and Jabari looks like a bust, while Embiid still hasn't played a single game.
So when you consider how good Butler is on both ends of the floor, and consider that he's only 26 years old, it's not at all unreasonable to make the decision to trade the pick and take the proven guy.
To me, the best way to look at it is this. Here are the #1 picks of the past 10 years:
Karl Anthony Towns
Andrew Wiggins
Anthony Bennett
Anthony Davis
John Wall
Blake Griffin
Derrick Rose
Greg Oden
Andrea Bargnani
Andrew Bogut
Out of those 10 guys, here is a list of the ones who I feel i would take over Butler in terms of pure talent (i.e. guys who either were better than Butler at their peak, or guys who have the potential to be better than him):
Karl Anthony Towns
Andrew Wiggins
Anthony Davis
John Wall
Blake Griffin
Derrick Rose
That's 6 guys out of 10, so that suggests to me that if you do get the #1 pick your chance of getting a player that is as good as (or better than) Butler is higher than your chance of getting somebody who isn't, and hence I would keep the pick.
But it's certainly not an easy decision one way or the other.