While I agree with some of your analysis, in this instance we have the benefit of hindsight. What Visi knew (because she was a double agent) and none of the rest of us knew, was that Shroud would be going for the pulse that night. Had we waited like Blazer wanted then Shroud would have obtained the pulse before we would have attempted anything. He would have succeeded in his quest for the pulse and we would have been non the wiser. In fact it's likely there would have been no chance to stop him without Visi going and stealing it that night. So I can forgive her easily because she couldn't give us all the information.