Your brain is the most personal possession that you have. If you believe in property rights at all you have to agree that nobody should be forced medication.
However, if someone is a risk to others ("or self" is bs because as one's own good is a subjective thing the individual defines what is and is not harm to oneself) then it may be appropriate to lock them up, and if there's a chance that medication (or other treatments, there is too much focus on medication, every interaction a person has whether with medication or conversation or what have you alters the brain in some way) would reduce their risk of reoffending then a case of offering a conditional parole could be made. Furthemore, there should just be prisons and voluntary mental institutions. Criminalize behaviors that show a person is a threat to others. And prison should be changed so that it's for rehabilitation rather than punishment.
As an adult who has already had the painful experience of forced psychiatry as a teenager, I believe it's all about how the person acts. If he/she is a danger to him- or herself or others, forced medication may help. I have personally never heard of someone receiving a forced injection, waking up, and remarking something to the effect of "Thanks. I needed that. I didn't know I was trying to hurt someone."