I don't see anything objectionable about the government you are proposing, the trouble is implementation. Eventually someone with corrupt intentions comes along and screws the entire thing up, or concerned mothers reduce some of our freedoms because "THINK OF THE CHILDREN". Politicians are fantastic at skirting their way established laws using loopholes and leaps of logic.
Ah, but these three things are the exclusive laws. That is, there may be additional, regular laws, but they must always be allowed by those three laws, much like how laws are supposedly supposed to be made in adherence to the constitution, which is a vague and highly subjective document. These, on the other hand, says clearly that if a law decreases total freedom, then it's illegal. It's not illegal to outlaw murder, because it increases the freedom from danger more than it decreases the freedom to get some healthy exercise. Banning dirty magazines is illegal because the freedom to communicate, freedom of expression, freedom of economic activity, and several others are greater freedoms than the freedom from having to occasionally parent your child.
All you need to do is say that "Your proposed law violates #2, your argument is invalid." Of course, if we're looking at building a new structure, then that would be easy to do. I'd say three overseeing groups, like senators. They are all elected the same way, and like the three branches of the US government, one group creates laws, the next enforces them, and the third makes sure the other two are kept in check and validate the laws. Engineering that structure at this juncture is a bit more work than I'm interested in at the moment, but after I have some tea I'll sketch something out on a napkin for you.
EDIT: added a bit to first paragraph.