Just to be clear; you can’t say something like “I could make a call on my mobile phone whilst driving (which is illegal), and then hang up with no one harmed” – because although in the specific instance no one was harmed, in the general sense someone could easily be harmed (if you lost control and had a crash).
But even the growing of the drugs yourself and smoking them on your own still does not really qualify for there being "realistically no possibility of anyone other than the agent in question being a victim or coming to harm", because if the effects of weed smoking in excess are true, then eventually for some people there will be negative externalities - if, for example, you end up imposing an excessive burden on the health service, or addicted to harder drugs, or becoming dangerously paranoid and volatile. If any or all of those things happen then others will feel the effects of your drug-taking. Here are some of the other suggestions I got (with my comments included):
My Comment: No, the victims are the artists/companies that are losing money through loss of revenue. Of course, there's no guarantee that they always incur a loss, if, for example, sales increase due to dissemination of information - but some will.
The only good one was, ironically, related to marriage. One contributor proposed the following; “A victimless crime is finding a way to gain the legal benefits of being married to a person of the same sex in a place where same sex marriages are illegal”. That's a good one; there I can see no reasonable grounds to call anyone else a victim. Cleary, as well, I think it is also ironic that the one valid suggestion put forward is one that most pressingly involves the need for a law change. This shows that laws are predominantly about protecting potential victims as well as potential felons.
* Gary Becker's famous rational crime theory involved weighing up the costs and benefits of crime, and trying to ascertain whether some instances of criminal behaviour are rational. For example, Becker considered whether parking in an illegal but convenient spot was a rational thing to do once the probability of getting caught is measured against the benefits of a convenient parking spot.Becker famously spoke of goals in the sense of our being rational actors engaged in a diligent cost-benefit analysis of whether crime pays. Some criminal activities involve reasonable goals if the benefit from the act is perceived to be greater than the probability adjusted weight of being caught and paying a penalty. Developing this David Friedman has argued that "The amount of the punishment should equal the damage done by the crime". The point being, that if crimes are committed when the value to the criminal is greater than the societal harm, only efficient crimes will be committed.