Someone's ability to organize should be based on their record within the organization they're working with. If drugs are interfering with their ability to help effectively then they should try helping in different ways or using the time they would be helping to fix the issue. Saying that someone who does drugs can't be a comrade is counter-productive. Revolution will always require the support of those labeled dregs and removed of society. People who work well within the current system aren't going to want to change it. Addiction can be one expression of a hate for this capitalist society, and working towards a better future can focus that hate into something productive, opening the door for sobriety.

As long as the person doesn't bear enormous responsibility we shouldn't be policing the way people live their lives. As long as they are effective within the org and aren't harmful to those around them outside of it they should be aloud to live their lives freely. Categorical no drug rules can also allow ableism to seep into the movement, which has been mentioned elsewhere in the thread.