In my experience, while it is very popular to say, difficulty rarely discourages a golfer or makes them give up the sport. I recently played Muirfield Village with a guy for business that shot 120 (mostly because he picked up). He knew that he was bad, but had never played a golf course like MV before and was amazed at how great the place was. Also, I could see new golfers absolutely loving Wolf Creek in Mesquite, NV, despite forced carries over desert and really difficult golf holes.
IMHO, 2 things discourage new golfers: (1) cost and (2) bad design. I think Peter properly addressed the cost issue. However, no matter how difficult his designs are, I don't think Nicklaus has discouraged many new golfers. Rather, a badly designed course is much more to blame. In particular, following my belief that typically the developer is much more to blame for a bad golf course than the architect, I think many residential lay-outs with holes that were created after the housing development and where the golf course acts as an ampi-theater to the homes on each side are to blame.
There is a course in Medina, Ohio called Blue Heron. It is one of the worst lay-outs you could ever find. It is full of 375 golf holes that you have to hit 6 iron off the tee in front of a pond and then hit another 6 iron to the pin. Plus, there are homes on both sides of most holes so there is no feeling on the course. I don't know who the developer or the architect was, but both failed miserably. 10 years later, the home sites are still half empty and the golf course gets no play. I am addicted to golf, but if I had to play that course, I would take up tennis.