I'm certain that the same flasks or condensors offered for sale to future scientists could also be used to cook meth. So what do we do? Outlaw selling chemistry sets?
There have been a number of cases of people getting into trouble because an interest in chemistry as regarded as suspicious. One kid even had to promise (I am not sure if it was legally binding or not -cannot find the article) not to do any more chemistry experiments at home, even though he had been cleared of doing anything illegal.
I am surprised that it is illegal to advertise prostitution: lots of print magazines in the UK used to do so, and Google lists prostitution web sites (probably organic only - it must be against the Adwords T & C).