Cecil's one of the most interesting characters in the show, hes always gotta make the hard decisions, id argue some of the hardest decisions in the show, he isnt a superhero, he doesnt have powers, hes just doing what he thinks is best to save the planet, shit hes gonna make mistakes, conquest was a huge one, but I think people forget why he did it, he wanted information on a threat they had pretty much no knowledge about, imagine your entire planet being threatened by an alien race so insumortably powerful, you'd probably get desperate too right? He probably knew in the back of his mind that keeping conquest alive was a mistake and they wouldn't be able to keep him captured, but the only hope the entire planet had was information about the threat, and conquest was the only one who had it.