My recollection of Leibniz's view is dim but I recollect that the essence of it is that the perfection of the world is a consequence of the perfection of God. It would reflect poorly on the Omnipotence, Omniscience, Benevolence & Supreme Awesomeness &c of the Deity and Designer if he bashed out some second-rate less than perfectly good (or indeed merely averagely awesome) world. For the benefit of the general readership, the book to read on this is Candide by Voltaire. You will never see rationalists in quite the same way again... :-)

I think this comment reinforces Will_Newsome's point. The textbook Rhetoric, Logic, and Argumentation: A Guide for Student Writers by Magedah Shabo (quite correctly) uses Voltaire's Candide as the very first example of a straw man fallacy on page 95.