Obviously everything any person does affects another even people beyond their own family and social circles. However, many states have raised the amount of marijuana one can have before it is criminal because of the rise in court cases related to such and the ways in which such cases can give rise to corruption within the criminal justice system. By doing so, of course, one could argue that this kind of change in the law is more aligned with DUI laws and limits.
Without a doubt, people do get hurt without helmets, but helmets are largely a personal choice. Riders are fully aware of the dangers.
If prostitution were not criminal and legalized, the health concern would be significantly lessened because laws would be enacted relative to the practice. This would also lessen the amount of human trafficking, violence, corruption and other abuses the current laws engender.
Even though gambling can become a habit, some forms of gambling are commonplace and do occur such as work betting pools on games, etc.
This is not to say organized crime betting and those affecting more people should be legalized or overlooked, this is just exploring the realities of society.
No matter what you criminalize or do not criminalize, we are all victims of something. After all,what is legal is not always moral. In fact, many behaviors that are "legal" are actually immoral and corrupt, by extension.