thats a lot of facts you ahve there to back up your opinion. do you have any idea what a flashback actually is? Seriously, the amount of brainwashed, propaganda filled jackasses is staggering. Now Im sure there are bad side effects and downsides to all these substances, and I think if people do try them to do it moderately. stay away if you can I guess, but everyones free to do what they want.
but more importantly, I just hate ppl who plain make shit up and pass it off as fact. The reason ppl get "flashbacks" is because of emotional triggers in the brain, and has nothing to do with chemical aftereffects. The closest think to compare this effect to is PTSD, or post traumatic stress disorder.
Basically, when you have a heavily emotional experience, a "stressful" experience (stressful in the scientific sense not the everyday usage) that memory and your experience is logged into a certain part of your brain. later on in your life a trigger can bring that memory flooding back up to the surface. This is not "another trip," there are no residual substances stored in your spine or whatever. this is just your brains way of remembering something. it is virtually harmless and does not reflect any damage to your brain or body whatsoever.