I'll say it straight up, there are some drugs that are bad for the body and mind but some illegal drugs could be good for people if given in a controlled manner by a physician. Some drugs are highly addictive and cause damage to the body and mind (e.g. meth, coke, crack, heroin) to name a few. However, other drugs, such as cannabis, do zero damage to the body and for many or even most people cause no harm psychologically even when used heavily. It is medically impossible for anyone to overdose on cannabis, and it is entirely possible for one to drink themselves to death and overdose on alcohol. Yet cannabis is still illegal.
Also, some drugs, such as MDMA, have important uses in psychotherapy. While I have never used it and have had no need to, it helps many people to get over trauma that they have suffered and recover from PTSD. However, the drug is still illegal even for therapists to administer. Additionally, psilocybin mushrooms have also helped many people to heal from mental health conditions when given in a theraputic setting, but it is impossible for people to get this treatment due to drug laws. Other illegal drugs have important medical and psychological applications but are banned by the law.
In addition, legal drugs, such as oxycodone, cause a lot of harm. However, they are still prescribed by drug companies regardless of negative effects that are far worse than their alternative that can be used in some cases (cannabis).
Drug laws also target minorities and other individuals that cannot get a lawyer. In many minority neighborhoods, people are arrested and jailed long term for using and selling small amounts of drugs. This results in voter suppression and the inability to participate in our society.
I had a good friend that got charged for selling a dime bag of weed to his cousin in a parking lot. Lucky for him he was white and able to afford a lawyer, but he was facing a felony charge (luckily he got it down to a misdemeanor). Had it not been for being able to spend nearly ten thousand dollars on a lawyer, he likely would have been imprisoned for a couple of years and would have lost his voting rights. If he were a minority or unable to find a good lawyer, my friend likely wouldn't have voted again and could be in jail right now.
Furthermore, some cops in minority areas go around looking to shake people down for drugs to get them sent to jail for their own sick power trips. I feel that the drugs laws are an active attempt to suppress members of society and keep those in power more powerful. In the case of cannabis (and maybe some other illegal drugs), the substance is not very hazardous. Yet it is banned in order to keep people from thinking from themselves and to be used as an excuse to send minorities to prison and prevent them from participating in society and having an influence in our world. That is why I feel every drug should be legalized.
Also, philosophically, I do not believe that drugs should be banned even if they are harmful. Some drugs are very harmful. However, even those that are should be legal because it is everyone's choice to do with their body as they please. Even if heroin and crack were legal, I wouldn't be smoking and/or injecting them. However, I think that if one chooses to make such a bad decision, the government shouldn't punish them over it. The person should instead be encouraged by their doctor and/or others around them to make better choices.
This has been proven to be a far better model. In portugal, where all drugs are essentially legal for personal use, use is down. Why? because doctors and even cops simply encourage people to give up their illicit vices rather than arresting them. This has caused drug use to drop and those addicted have easier access to rehab/detox facilities to get clean. When an individual is arrested for drug use, it causes them to lose connections with society and actually ends up encouraging drug abuse rather than discouraging it.