Does the words I highlighted in blue refer to "marijuana"'s users are as small as the toothpaste of the tube? If no, what does it mean?I believe marijuana is not so harmful to society as to justify locking up users, but it remains harmful enough that it can be a valid public health concern due to concerns of stoned drivers, use by young people etc. As such it ought to be tightly controlled. Libertarians will respond asking if I favor a similar system for alcohol or tobacco and the answer is that alcohol and tobacco have already sufficiently penetrated our society and widescale commercial production is widely accepted. The toothpaste is out of the tube so to speak. Yet marijuana remains largely associated with a minority counterculture.
Is it an idiom?
not a teacher
"The toothpaste is out of the tube …"
This usually means that what has happened cannot be reversed, in the same way that once the toothpaste is squeezed out of the tube, it cannot be put back in.
In the context of your quote, it means that what is already well established cannot be changed in a major way.