Nice edit. Was about to respond to the previous..
...I rethought some things. =P xD
It has the same use nicotine and alcohol have. As long as they do it in their house and don't harm others, it's their problem and their choice.
But, Phoenix, the growing problem is that some don't do it in their home and harm others. =/ (Or, if they have children or siblings, the 'effects' might cause them to hurt their family in their home)