Oh, I misunderstood you. I was under the impression that that was the role to which you restricted the state. So what do you believe to be the proper role of the state?
I dare to mention it, but you seem to have come full circle on the concept of rights, perhaps a clarification on your part?
I'm a Thomist. I believe the state's duty is fostering the common good. That includes protecting God-given rights, enforcing social obligations, and outlawing vices from which it is possible for a majority to abstain, among other things.
As a Thomist, I reject the notion that there is such a thing as a right to vice; only a right to virtue. There is no right to drug abuse, no right to pronography, no right to prostitution, no right to to adultary, no right to fornication, no right to sodomy, etc. The state is perfectly within its competence in restricting these things. The question is one of prudence: does prohibiting such things help or hurt the common good? The answer to that is sometimes yes and sometimes no.
Here are a couple Summa articles that deal with this question:
http://www.newadvent.org/summa/209602.htm
http://www.newadvent.org/summa/209603.htm
I would recommend the whole section on Human Law, if you have the time.