HSS:
No, that is not accurate at all. Since only half the children of a 1 carrier marriage will be carriers, we will at most ever end up with half of us being carriers- which would work fine.
However, since less than half of us are carriers now, there is no reason why the carrier group will grow.
(Imagine a group of ten people whose descendants will intra-marry. Two are currently carriers. Each marriage will have 4 children.
The second generation is twenty people, of whom 8 are from a 1 carrier marriage. Of those 8, 4 are carriers.
The third generation is 40 people, of whom 16 are from a one carrier marriage. Of those 16, 8 are carriers.
So you see, the ratio remains the same.)