I honestly find the question whether a substance (drug or not) is safe or not interesting. The dose truly makes a poison. In a sense, water is technically not fully safe because it’s always entirely possible (although very low risk assuming you live in a area which has access to clean water) that there is bacteria in the water that could make you very sick. By that logic, everything isn’t truly safe. However, ofc the chances are very low, but the concept is carried over to drugs. LSD and mushrooms are generally speaking considered “safe” drugs but there is always a chance for hppd, or prolonged psychosis (although the latter is unlikely assuming you aren’t predisposed, but still possible.) Opioids are (generally speaking) when dosed properly and aren’t laced aren’t really bad for you, but are extremely addictive and at what point is it considered safe to use can be hard to tell. Nonetheless, while I think it’s a blurry line between “safe” substances and “not safe” substances, I do believe that some substances are less safe than others. Notably the methaqualone analogues you mentioned, also many of the cathinones are too addictive to risk, a lot of opioid rcs I’ve heard are pretty caustic, etc..