It is one thing to pass a law, it is another to enforce it. If only a few people disobey it, they can be prosecuted. If many do, the capacity of the courts and, if necessary, the prison system, can be overwhelmed. Furthermore, juries will be less willing to convict, and prosecutors will find they have more urgent business. Finally the law becomes an anachronism, on the books yet not really part of the living law. But damage has been done, in that there grows to be a distinction between laws we as a society mean, and those we don't.
Our most famous example of this process was the "noble experiment" of liquor prohibition. It led to bath-tub gin, widespread smuggling, speakeasies, and general disregard. It did not do much to address alcoholism. Indeed, by making alcohol a mark of personal rebellion, it may have increased it. Treating alcoholism as a medical and psychological issue seems more effective.
Something similar is now occurring with respect to marijuana. For years, prosecutors have given up enforcing laws against the possession of small amounts of marijuana, perhaps in the recognition that a typical jury of 12 will probably have a couple of jurors who quietly use it too. So now a group of states permit medical marijuana, and Colorado and Washington state permit recreational use. There is still a federal law on the books, but prosecutors find the enforcement of other laws to be a higher priority.
What can be said about abortion in this context? Before the Supreme Court decision in Roe v. Wade, there certainly were abortions in this country. They were illegal and often done in non-hygienic conditions, but they were done. The current moves to make abortions more difficult or expensive to obtain legally only increases the demand for illegal, under-the-table abortions.
Laws against gambling have pretty much gone away, driven both by the desire of state governments for new sources of revenue, and by the recognition that gambling as a business needs regulation to ensure against fraud.
A similar discussion surrounds gun laws. A law making it illegal to own a gun would be unenforceable. However, I think we can agree that citizens should not have the right to possess nuclear, chemical and biological weapons, artillery, or missiles that can destroy airplanes. What we need to discuss are machine guns, AK-47s and their cousins, etc. We need a balance between liberty of owning guns, and safety from their use by the deranged.
As a society, we are sometimes misled by a clamor to regulate other people's lives. These efforts often fail, even after enactment. Wise legislators should understand that what works is an empirical matter, and should adjust their legislation accordingly.