That was the rhetoric spread by drug dealers and fear mongerers in the early days. People are afraid of new things and tend to hype up the fear out of caution which I can't blame anyone for. Stoners arent exactly the most scientifically minded group of people in the first place either which doesnt help. That's what I first heard too. If you bother to do any kind of reading on the subject you will find its not like that. Delta/thc8 is naturally occurring in cannabis albeit at low amounts. It is essentially the same thing as delta 9 the main psychoactive cannabanoid in cannabis with the exception of one molecular tweak. Delta 10 is yet another variant of THC with one molecular difference too but is indeed synthetic due to it not being naturally occurring. While its hard to say now if these minor differences make any difference to health in long term the general consensus is "probably not" since the chemicals are so similar and essentially interact with the brain receptors in the same way. Its not like how with salt one sodium molecule makes a difference between poison and tasty rock. This stuff has been on the market for a while now tested by millions of people and nobody has reported health issues. D8 exist naturally in dope anyways so people have been ingesting it either way.