There was no perfection mentioned. Reducing the chance of a child getting drugs does not guarantee or suggest perfection. There are many many ways a child can screw themselves up. Lets not add one MORE thing to the things that can destroy humanity, such as the decriminalization of drugs.
Perfection and goodness are the same thing, btw. Goodness in the absolute is the only concise definition of the word, and hence true goodness is perfection. By the same token, perfection in the absolute is the only true perfection.
Only a moral relativist believes in relative goodness.
There is no goodness whatsoever in illegal drugs.
What you are really saying is, don't let protecting the human quality of life and it's long term survival impair whatever morally relativistic habits you have because you lack the character to strive higher.