So... let me get this straight: There is this Meteor coming to town which is gonna destroy all life as Alexanders knows it and Shinra has a plan to blow it up. Hearing about the plan Cloud and Friends (yes, actually it's Barret and Friends at this point, but Cloud doesn't stop them) steal all the Huge Materia which is the essential part of that plan because they don't want to see the Huge Materia destroyed (hey, it's the Huge Materia or every living thing on the planet, the choice is obvious), they even go (granted, accidentally) to Space to retrieve the last part of Huge Materia.
Now the rocket which was the carrier for a bomb crashes into the Meteor without the bomb and that obviously does jack trout to the Meteor.
And afterwards they stand on the Highwind and discuss how Rufus' plan failed... that they thwarted? What incredible assholes are they?
And don't give me that "They knew the plan would fail!" - no they didn't! Barret actually says he hoped it would succeed, which of course it couldn't because they stole the Huge Materia.
As I'm playing the game right now, I am pretty sure they had no plan of their own how to stop the Meteor - which leads me to the conclusion that they are bastards who just don't want anyone else to save the planet even at the cost of their and everyone elses lives!