Ok guys, I think everyone's missing the point of me and The Angry One here.
Here are the facts.
1) The Crucible is a device that is designed to stop the Reapers
2) The Catalyst created the Reapers
3) The Catalyst needs Shepard to activate the Crucible
There is absolutely no evidence that the Crucible will do what the Catalyst tells you it will do. You are only taking his word for it and it is the word of the creator of your enemy.
Look, I know, people are saying, "the Catalyst has no reason to help you, but he is anyways so that must mean he's telling the truth." Guys, do you not see the irony in that statement? Someone who is trying to helping you would make you put your guard down. It's called deception. Would you go into the house of someone that threatens to kill you or the person who offers you free cookies?
Now you could then say, "But why didn't the Catalyst just leave you on the floor bleeding then." It's because the Catalyst needs you to activate the Crucible. He says that so himself. So he feeds you a bunch of lies of what does what, and then you activate the Crucible and then it makes everyone indoctrinated so that they all stop fighting, and now the Reapers are free to turn the races of the galaxy into even more Reapers. Or maybe it freezes all the organic races in place while the Reapers harvest them. What it does is not the point.
"But wait," you say, "That never happens." You're right, it doesn't happen. But that doesn't mean it couldn't happen, and that is exactly the point. Everything I just said is something that Shepard could infer by himself. It's something that requires no meta-gaming at all.
The only reason everyone here is defending the Catalyst and how he must be telling the truth is because they know what happened. They know that the Crucible does exactly what the Catalyst says it did. But Shepard didn't, all he knows is those three facts I laid out. Shepard doesn't know if the Catalyst has to tell the truth. Shepard doesn't know if the Catalyst can alter what the Crucible does. So yes Shepard could take the leap of faith and use the Crucible, and it saves the galaxy. Or he could use the Crucible and it leads to a fate worse than destruction, such as the organic races becoming a Reaper. These are conclusions that Shepard could come to, so what would Shepard do, trust his enemy and hope it works, or die fighting?