First, even if 'negative' claims win by default, a positive argument for the truth of a belief is rhetorically stronger. The world is not perfect. If something is created by a perfect being, it is perfect. Therefore, the world is not created by a perfect being. As for the first premise, nothing is more certain from all human experience than the fact that the world is not perfect.
Bad stuff happens.
Natural disasters rip apart the fabric of entire communities. Diseases bring slow and agonizing deaths to people. People could be better designed to handle these things and accomplish more, but we are frail critters on a speck of dust in a capricious universe. There are no degrees of perfection. B. It would be better if an imperfect thing weren't created.