Where do we draw the line - by Prison Widow Global

So we've had an interesting collection of emails this week! Some people agreed with sanctioning prison visits if drugs were an issue and some strongly disagreed saying that family contact was paramount. So where do we draw the line? Or is there any line to draw? 
Children who are raised around drugs here on the outside can suffer from experiences that will leave them mentally and emotionally scarred. We've already covered topics on how children are affected by drug/Police house raids. Some of the stories are heartbreaking.
So when their Mum or Dad faces a custodial sentence off the back of those raids - is it acceptable to still visit a parent in prison who continues to use substances whilst serving their prison sentence? It's a tricky one isn't it? My take on it would be that I wouldn't be putting my children through anymore trauma and let's have it right; if a person uses drugs in prison, it is highly likely that they are going to quit on their release. In a nutshell; no, families cannot reduce reoffending if their loved one is an addict and the addict is not ready to kick their habit. 
Would there be an impact on someone in prison having their visits sanctioned? Yes; they would probably use more drugs to cope with the fact that they can't see their families; but hold on a second - they are using drugs anyway even after family visits! So again my question is; Where do we draw the line?