Re: Harbour Town and Cypress Point : environmental rules clearly stipulate that you can't always build what your eye envisions on a given site. [In fact, you might not be able to build on that site AT ALL.] But, there might be somewhere else where you could build exactly the same hole and it would be okay.
Re: safety issues such as #7 or #17 on The Old Course: holes similar to these could be built and enjoyed by golfers, if the owner of the course is willing to deal with the liability issues they cause. That would be a very rare owner in today's world, but it is NOT an absolute. In fact, I've got a plan on my desk right now for a course with crossover tee shots. The owner does not expect the course to receive a lot of play, and the safety issues are less severe than on 7 / 11 on The Old Course, so he is not too worried about it, though we both understand it might have to be modified in a few years if he wants to open the course to more outside play.
Melvyn is right, that people in the modern age are too quick to dismiss good ideas for boilerplate reasons. If it's a really inspiring idea with a problem, you should think really hard about whether the problem can be addressed, instead of just giving up.