The AMA was founded by doctors. It's main purpose is to promote the welfare of doctors. That is not good or bad thing, but it is a very useful to keep that mission in mind when you hear the AMA speak.
The first question I would ask is that if the AMA is really concerned about health care costs, why does it not push harder to make more drugs like birth control pills available over the counter without a prescription? Or streamline the prescription process for drugs that low potential for abuse or for causing harm (most ED drugs)?
The second question I would have to ask is why is a better-informed consumer a bad thing? If the ads are incorrect or misleading, that obviously need to be addressed, but other than that, why would a patient hearing about a possible new treatment option be a bad thing? Are we not supposed to ever question our doctors? Is a doctor's time really so valuable that they cannot explain treatment options?
There are some serious 1st Amendment issues here as well. 30 years ago, you could have made the argument that public airwaves are a limited resource and that the government should have some say in their use. With cable, that is no longer true. You really have to show that drug ads are a major concern for public health like the cigarette ads were. The fact that drug ads annoy doctors is not a good enough reason.