I think that the halucinogenic component of a marijuana high can permanently alter one's perception of the greater world, perhaps not always in a positive way. While I cannot say for sure, I do feel that my ongoing issues with depression and paranoia can be partially attributed to my years of heavy pot smoking. If (psychologically speaking) you're not cut from mj-smoker cloth and you try to make as if you are, I think the long-term psychological effects can be very damaging.
But, I know that not everybody is like me, just giving my $.02.