User blog comment:Braveangel/About planetary defenses/@comment-2006054-20100423051350

Remember how Destiny Ascension was crippled in the opening moments in the battle of the Citadel? It is because the Citadel is located very close to a mass relay. Any invading fleet would pour through the relay: dreadnoughts, cruisers, even smaller classes of warships. And they would immediately engage the Citadel fleet in knife-fight range. And dreadnoughts are useless in that kind of battle.

Having platform-based defenses would be like having sentry turrets in the geth station working for Shepard to act as first line of defense against the incoming geth waves during the final battle in the Geth's Headquarters. They are easily overpowered, but can reduce the strength of the attackers just enough to help us win the real battle.

And even when the Citadel is run by the keepers, the Council races are technologically advanced enough to install any system on top of the existing system. Maybe the new installment would have to have its own energy generators and targeting system, but I think the Council can afford the tech and the cost.

But if the reasoning is that lacking planetary defense is an 'integral to the plot for the Citadel to be unable to handle the attack of Sovereign and the geth"... well, that doesn't make sense to me. Why do they have to be the fools just to make room for some plot? That, by definition, is a plot hole.

And Horizon is not by any means "unnoticeable". It's a garden world that is a "sweet spot" for carbon based life. And we know that the batarian pirates usually target human garden worlds in their slave raiding operations. Sooner or later, as the colony planets within the Alliance space are better protected, the batarian pirates will target human colonies in garden worlds in the Terminus system, closer to their own "hunting ground". If not against the Reaper or the Collectors (that would be improbable because most of the people of all races don't believe that the Reapers and the Collectors even exist), the human colonies in the Terminus system should have planetary defenses against batarian pirates.