Not all in the Alliance Command thought it the best course of action. The idea of the Death Star left some too hopeless. [he's familiar with that, but it never quite stopped him the way it did the alliance leaders.] Some of them thought it was unbeatable.

The flaw was built into the system. The plans were needed to exploit it. We went in to steal them, because no one else would. [and he felt like he'd done so many bad things before then. it was personal amends, in a way. he'd said himself to jyn: he wouldn't have been able to face himself if he gave up. he saw what happened to jedha firsthand. there was a chance to stop it, and rogue one took it.]

You can imagine how relieved I was to hear it had been destroyed.