An important question and one the legislatures of this country should consider.

Do laws such as the New Mexico law against cohabitation, which serves no useful purpose for the government, and remains unenforced, cause people who find out about them and happily violate them to gain a lack of respect for other laws? Does it add to a cynicism that the law is not anything worthwhile?

I personally feel it does. The wide variety of laws present across this country that attempt to regulate all sorts of aspects of peoples' lives that are pretty much uncontrollable discourages people, causing them to think the lawmakers just want to make laws. Laws against who we can sleep with in our homes, laws against which sexual positions can be done (last I knew there were laws in some states forbidding sex except in the missionary position), and other similar laws which make things that do not harm anyone illegal encourage people to laugh at all the laws.

Maybe what the government needs to pass is a law requiring that there be a definite reason for any law passed, and that it must serve the interest of the government and people.