You obviously haven't spoken to many older stoners. I know plenty of people in their 60s and 70s who are just fine smoking a joint or two every evening instead of alcohol. To them, the high hasn't changed so much that they don't enjoy the experience. I get the impression you're prejudiced against cannabis simply because of your own negative experience.
Not only my experience, but the experience of countless other people. The OP may have gone too far in claiming that this happens to every weed smoker. I never said that. I know there are people who have been smoking weed much of their lives. I have met people like that. But for every 50 year old stoner you talk to, how do you know there isn't another 50 year old person who used to love weed in their youth but either had to stop because they started getting negative effects, or just stopped getting a pleasurable high from it? I mean, even the Grateful Dead describe this. Don't any of you listen to the Grateful Dead?
What in the world ever became of sweet Jane?
She lost her sparkle you know she isn't the same
Living on reds and vitamin C and cocaine
All her friends can say is ain't it a shame
I don't know how you guys can go on denying it, when there are so many people saying this happened to them. Just google "Marijuana anxiety panic". Statistics also show that most marijuana users stop smoking by their late 20s. If the high didn't change, and it remained just as enjoyable as it always was, why would most people stop using it?
I remember when I first started smoking, I used to hang out at my dealer's house and we'd all get blazed except for this one girl who would never smoke with us and would always drink instead. One time, my dealer asked her why she wouldn't smoke weed and tried to explain to her how much better than alcohol it was. She said "I used to smoke all the time, but then it started making me anxious and paranoid, so I switched to alcohol" and my dealer (a heavy stoner himself) gave her a knowing look and said nothing more on the matter. He did not say "What are you talking about bitch? Da herb is a gift from God", he accepted her answer completely. It was obvious to me at the time, that he knew something I didn't know, because back then, as far as I was concerned, anyone who freaked out on weed, was weak minded and needed to learn how to handle an introspective experience. Years later, when weed finally turned on me, I remember thinking back to that moment, and understanding.