Suicide Risks and the Sales of Paracetamol... Example of the Ignorance of the Law?

Ok, so I was in the store the other day, and I was refused to serve because I had 2 packets of paracetamol... I was so confused, I spoke to the manager who informed me it's now illegal to sell more than 1 packet to anyone, because of a risk of misuse! I then made him speechless by stating that I could legally buy gallons of Vodka and Mountains of tobacco and do it that way... and yet this was illegal. 

Ignorance of the law? In that it is not only a massive inconvenience of some unconvincing evidence, it's ignorance in that if those determined to misuse will simply get a friend to buy more or go to a different checkout... Lastly in that paracetamol should be the least of our worries.