The only argument I ever see working for the DLC cons is why pay for something that is already made and in game? If they didn't get enough time to finish certain characters and we are basically paying for the extra time involved I am all for it (hell I wish I could pay for better netplay while we're at it).
Some companies though charge for a couple of characters they already completed by the time the game is out. This, in my opinion, is B.S.. If you need to charge more money from the start then make the premium release with an exclusive poster or whatever that cost a buck to make and charge 10 for it. Most gamers will thank you for it anyways.