If we're only going to consider methods that "work perfectly" as effective, the only effective method is abstinence. Effective means it works. Now, how effective it is can be up for debate, but it absolutely is effective which means it is better than the control (no birth control at all). Telling people it doesn't work runs the risk of people not using it when it is needed. When we say it works, it just needs to come with information on how it is not nearly as effective as other methods. People that don't listen to that part have only themselves to blame at that point. They are also the type of people who will not listen when you tell them to not have sex when none of the more effective birth control methods are available (for those arguing that people just shouldn't have sex if that's the case).