I guess I should have also stated this...
I think the USGA/R&A have always laid it out fairly simple. In their view, if you accept money for your likeness, for teaching, or for prize money, you have violated their definition of amateurism. If you do violate the rules of amateurism, you have to apply for reinstatement, and wait a period set by them to regain your amateur status. Obviously, there is a blurred line of sorts that is hard to judge. I am playing a US Mid-Am Qualifier this coming Monday with a person that has played in majors, had a PGA Tour card for a short time, I'm guessing made considerable earnings on the Tour, led the Order of Merit on the Asian Tour for a season, etc. He didn't play professional golf for 10 years before being reinstated though. I'm personally ok with that. I know there are a lot of guys that aren't. I also realize you have to draw the line somewhere and I think the USGA has done a good job of determining that line for the vast majority of cases. This belief in some code that exists, or existed, where once you turn pro it's forever, is simply unfounded and based in myth.
To get on topic in some small way, I think the addition of two mid-ams to the Walker Cup team is refreshing and I think Scott Harvey was definitely deserving of one of those two spots and Mike McCoy's resume is super deep and deserving of an opportunity to play on the team.