The federal government doesn't necessarily need to fund the residency training of doctors, but if we want more doctors then that's the fastest way to get them. Most teaching hospitals are non-profits so if they had to self fund residency programs then they would have to raise prices to patients. Hospitals barely break even (or less) on many Medicare service fees so those don't provide much margin to fund residency programs. That is the reality of our situation regardless of whether you trust the AMA.
Yes the American Petroleum Institute is a good source of information on some topics. They're certainly biased and I disagree with some of their conclusions, but they publish some accurate data and it's worth understanding their perspective.
If you're talking about clinics catering to poor populations. Why can't they use their Medicare money?
I'm sorry, I don't trust anything from the AMA because they are a lobbying organization. Why don't I just start sending links to the American Petroleum Institute while we're at it?