True Catholics are libertarians because politics should mirror the Church, and saving one's soul is based on PERSONAL RESPONSIBILITY. A nanny state cannot force anyone to save their soul or to follow laws.
Even St Thomas Aquinas said that prostitution should be legal, but follow zoning laws, because no amount of govt regulation would ever stop it. So you use zoning laws to regulate it to an isolated, rural part of the city which moral people can avoid.
People who smoke MJ are gonna keep doing it, laws or not. You might as well legalize it and make it safer.