While willpower can be exhausted, it's also possible to increase willpower reserves via such things as exercise and meditation[1].

Personally, I think promoting education and awareness (and providing training) to people wishing to improve their willpower would be preferable to further empowering the immense coercive apparatus of the state to interfere in the minute details of our lives.

People lacking willpower will always find ways to self-sabotage, so helping them increase their willpower would be far more efficient than trying to ban every single thing that their poor willpower could render harmful to them.

1. http://scopeblog.stanford.edu/2011/12/29/a-conversation-abou...