Okay. I'll start off by saying that is not a "moral fact" that drugs should be illegal. If they are against your morals, that is absolutely fine but a fact it is not. Applying your own logic to the fact drugs alter chemical balance and therefore should be banned should then mean that all hospitals and doctors surgeries should stop using medicine (drugs!). The fact that they are "bad for your body" means all foods and drinks deemed unhealthy should also be banned, right? People should only be consuming things objectively good for their body?
It could be argued that most people that want to take drugs already do - for the most part they are not that hard to obtain. Anyway, if drugs were to be regulated, I think there is no doubt that some people that have never taken them before may try some out, correct. However, it is hardly likely that a huge wave of people will suddenly turn into avid drug users just because they are legalised. Most people already have their own limit of what they would take and would not take (you are a great example!).
Legalisation/regulation would decrease overdoses. The regulation of drugs means that purity and dosage can be controlled and people will know what they are getting. This makes it much safer.
Legalisation/regulation would decrease violent crime. If drugs are regulated by the state, it cuts out the middleman. Where do people currently buy their drugs from? Dealers and gangs. Where does most drug related crime come from? Dealers and gangs. Regulation pushes them out of the market. Addicts on some of the much harder drugs, such as Crack and Heroin also resort to [violent] crime to fund their habit, right? With regulation, money that would have been spent on the 'war on drugs', and money made from selling the less harmful substances could be used to setup clinics to help these people. Substitutes and a safe place to take their fix could be readily available to them, with professionals able to give them the help they need to steer them on to the right path/recovery.