Vice
While vices of all kinds are generally dangerous to individuals, they are a vital part of a Just Society. Many people struggle to learn from others and need to make their own mistakes to learn for themselves. For many of them, vice is an essential part of their journey to become better people and draw closer to God. Banning vice to keep it away from these people might look appealing at first glance, but denying them the ability to learn only hurts them in the long run.
It is true that not everyone will overcome vice, especially during hard times, but that is the nature of tests. Only trivially easy tasks are accomplished by everyone, and the lack of struggle robs them of any meaning. True growth requires struggle, and by definition not everyone succeeds. Help should be provided, but some people would prefer to be consumed by addiction to vice than face reality, and they cannot be saved. Even if they were forced to avoid all vice and go through the motions of piety, it would be an empty life devoid of virtue and doomed to slide into damnation through apathy.
Banning vice is not protection, but slavery.
The proliferation of vice is also a vital feedback mechanism for a Just Society. Vice rises in hard times, so monitoring usage, for example through sales numbers, can reveal problems and allow them to be resolved quickly. Drugs are commonly used to numb the pain of economic struggles, while men turn to pornography as a substitute when acceptable women are unavailable.
The correct response to rising vice is not to ban the vice, but to investigate and resolve the underlying cause of that increase. Attempting to ban the vice in question only blinds society to the true problem, and criminal organizations will rise to satisfy the demand, making the situation even worse.
Thus, a Just Society recognizes that vice is a necessary evil, and that discussions of responsible usage are an irrelevant distraction. At a large scale, tracking the use of vice is a vital feedback mechanism to identify problems, and at a small scale, people must be free to make mistakes so they can find their way closer to God.