First, it is important to consider the definition and meaning of the term "victimless crime." These are usually defined as activities that are illegal, such as prostitution, but where there is no "victim," since only consenting adults are involved. In other words, the claim is that nobody's rights are being violated, since conscious, adult choices are made by all parties involved.
When looking a little closer at prostitution, on might question whether this crime is truly victimless. Indeed, can it be regarded as a form of domestic violence? The background of those who make use of prostitution services can shed some light on this question. Supposing that the man is married, one might consider the fact that his marriage, and by association his wife, fall victim to this crime. However, should the wife also have given her consent to use a prostitute's service, the crime could be considered victimless, since all parties are aware of what is being done and everybody gives consent. Also, if a man (or woman) making use of a prostitute's services is unattached in terms of a romantic relationship, one might consider the crime to be without a victim.
Another interesting angle to consider is if the prostitute has any loved ones or romantic partners who might be considered emotional and/or domestic victims to her crime. The argument in this case might be the same as above: The crime is victimless when there are no parties who can experience any kind of potential distress because of the activity.
In the case of gambling, the argument is the same, although the specific medium of abuse is money. In the case of compulsive gambling, the gambler might be using household money to feed the addiction while the family sufferes as a result. This could be said to be a form of domestic abuse.
On the other hand, if the life partner or wife is part of an occasional outing that involves some casual gambling, the consent of all parties involved makes the activity victimless. Also, if all members of the family have given their consent, even if they are not all physically involved in the activity, it might be considered victimless.
Some critics have campaigned for the decriminalization of victimless crimes. This would provide, they say, for more funding availability to prosecute truly heinous crimes more effectively. Others have debated against this, citing the moral and legal fibre of the country as far more important than the actual number of visible victims of criminal activity.