As the game is set up now a stellar converter can be used against a planet that has infinite defenses and fleet defenders. A single ship can move in and without initiating an attack it can blow up the planet with impunity.

I have a huge problem with this. Players should have the opportunity to defend their systems if they have any defenses at all.

Agreed! I always attacked first, figuring I would need to destroy the defenses before I blew it up. Thanks for finding this.