At the end of season 1 for Justice League Unlimited, a conversation occurs involving the cannon on the watch tower. One of the original 7 members justify the presence of the cannon by pointing out how it would have been useful against the Thanagarian invasion (which occurred during the last episode of season 2 of Justice League), as it could have been used to destroy the hyperspace bypass generator.
But I simply don't see how the cannon would have been useful. For one, Shayera Hol would have been well aware of the cannon if it existed on the watch tower during the Thanagarian invasion, which means the Thanagarians would have had just about every detail about it. This would have led to two possibilities: 1) the Thanagarians would have utilized it as one more weapon to keep the Earth under control or 2) recognized it as a significant threat if they were to lose control of the watch tower and disabled/destroyed it. In fact, they could have benefited from both possibilities: actually destroy it, but use the threat of it in civilian areas to deter the Justice League from a wide range of actions.
In reality, the cannon, which is essentially a space-based weapon under no government jurisdiction, winds up being a significant factor in how the populous negatively views the Justice League during the course of Justice League Unlimited. So, considering the questionable benefit and the very real drawbacks to the JL's public image, how did the members of the Justice League think the cannon would be beneficial overall? Do we know how each member of the original seven felt about it?