I don't want to highjack this thread and talk about the intracacies of playing dragon but there are a lot of ways that you can cast animate dead, target worldgorger dragon and not win the game.
In such a situation, is it ever the right play to cast the animate dead?
What he is saying is when you cast Animate Dead on the Dragon and start the loop there are many ways to screw it up due to play mistakes. This will cause you to not be able to stop the loop which leads you to have to accept a draw with an opponent. Then there's the worse loop error where you have to pass priority and your opponent kills you all because you messed up the loop pattern.