@zerowole I can sympathise about your attitude towards drug use however your sister's case has no bearing on whether drugs should be legalised or not. It sucks that people make bad choices but as your sister has shown people will make them anyway. A lot of people suffer because their parents are alcoholics but that does not mean we should ban alcohol.

Not everyone who takes drugs is an addict, same way that not everyone who takes alcohol is an alcoholic. The banning of alcohol and then it's subsequent legalisation has shown that prohibition does more harm than good. It also wastes vast amounts of money criminalising people instead of giving them treatment.

Maybe your sister has refused treatment in the past or maybe she has failed because she is unable to cope with life without drugs.

I don't know her specific case but I come across a lot of people who found it almost impossible to give up in the throes of addiction.

It is an illness and should be seen as such. An addict is unable to make rational decisions. That is not and never should be a basis to make decisions about the rest of the population.
That would be like banning peanut butter because some people have peanut allergy.

I also don't think you should ever give up on your sister but that is for you to decide.

I have known many people who were unable to change after being given multiple chances and seemed like they were completely lost.

Then for whatever reason, something changed, they realised what they were doing and had some kind of epiphany which enabled them to accept help.

It was never a completely smooth road but many of those people have succeeded in fighting their addictions and starting the path to recovery and remission.
It is rarely (if ever) too late to change.