Society cannot guarantee that 100% of the population will have no reason to commit crimes. Even something as fundamental as not agreeing with a certain law can be reason enough to break it, as seen in the case of civil disobedience.

When we talk about the reason to commit crimes, we're talking about intent, the very first stage of violent crime. That's the part where someone convinces himself that it makes sense to use violence to get what he wants. Of course, the less intent people are on committing crimes, the better. However, at this point, violence is not happening yet.

Violence comes into play during later stages, when the criminal is actually making his move. The purpose of the threat of violence is to convince people that it's in their best interests to behave according to the rules. Warranted use of violence exists to convince criminals that things could end up very badly for them should they choose to escalate the situation.

Violence is what you use to make unwilling people do what you want. Robbers use overwhelming violence to make victims give up their belongings. Cops use overwhelming violence to make the robber surrender to arrest. If someone is being judged in court, what stops them from literally getting up and walking out to freedom? There are police officers there who will violently prevent that from happening.