I'd be interested to see the data on this, because I suspect occasional use (i.e. less than once every 2 weeks to one month) is not as damaging, if at all.

Occasional use is very different from the "wake and bake" style of using marijuana every hour or so. I fell into the former category, as did some friends of mine, but I knew many who were in the latter. The differences a few years on are quite profound.