Example - a weak-willed individual who will, if drugs are legal, become addicted. That is he needs the force of law to keep things in line. That doesn't impress me much. If you are determined to self-destruct no amount of laws will save you. And regarding drugs, there are many treatment programs available. All our addict would have to do is to check in to one of them.
Bottom line is that people very often depend on govt to do what they should do themselves or could do with assistance from civil society.
One step further, if you will: many of those people to whom you refer also want to place everyone else under increasingly tighter government control. They can't handle their freedoms and don't believe that others can either.