I definitely think an avid golfer can design a solid, even a GREAT golf course. On a world class scale, you don't have to look much farther than Pine Valley, Merion & Pebble Beach. I realize that George Crump had input from some of the very best "experts" of his time, but much of what Mr. Crump created at Pine Valley, he did on his own. His "amateur" vision of what Pine Valley could become, led to one of the best golf courses in the world. I realize that each of these courses have been touched by a professional in some way, but I don't think it discounts the fact that these "amateur" architects had the ability to create something very special.
An a smaller more local scale here in NJ, avid amateur golfer Archie Struthers created what many regard as one of the better public courses in NJ at Twisted Dune.
I've played plenty of awful courses over the years, some designed by the so called pro's. There is no question that a better course could have been designed by an amateur.
It can be done...