LSD and similar hallucinogenic drugs act on serotonin receptors. At some point you'll need a higher threshold of the drug to experience a similar effect. LSD may not directly destroy brain cells but it doesn't need to do that to fry your brain. It fries it in the sense that it messes up important receptors, which in turn become a detriment to other neurotransmitter pathways, leading to the so called personality and behavior changes you describe. So yes it still physically screws your brain, just not in the most destructive way possible to where you no longer have cognitive function. If your going to make statements like you are, be clear about it. I assume you are a teenager with your constant mentioning of the ACT. You have a lot to learn still so don't make blanket statements and go off what your one hipster friend said or what some random article indicated. Look at scientific papers to see where research is at on these topics. Also once done, the drug is theorized to stay in your system, leading to what some people experience as hallucogenic flashbacks. May happen to some, and not to others. There's still a lot to learn about how hallucogenic drugs affect the brain. So no it is not really safe for anyone to take in any amount unless medically needed.