I can totally understand how someone would sort of think of it as "free" or as in you've already paid for it, so now it is just a matter of sharing what you own. I really wanted the company on my first trip but....
I had no hesitation in explaining the points system in detail to my sister and would for anyone who was going to come---it's not so much that I don't want to freely share, but I prefer to be up front and explain the cost in terms of points. True, you are sharing what you would be paying for anyway, but you may also be limiting yourself to less time on your own. Anyway, if any gift is sort of taken for granted, I think it would be disheartening to invite people.