There's really no reason why diffuse harms should not be criminal while focused ones should (arguably, diffuse harms are less able to be addressed by individual action through the civil justice system, so outside of focused harms where the victim is unable to pursue action after the crime, like murder, diffuse harms are the most important for government to address directly.)
OTOH, there's often a lot more disagreement over whether what some people perceive as a diffuse harm actually is a harm.
For example, dumping mercury into a major river causes extremely diffuse harm, but I'd never describe it as a "victimless crime."
In the other direction, smoking weed in private harms nobody except the smoker. The harm is so focused it doesn't even touch anyone besides the offender. Yet this is almost the canonical example of "victimless crime."
It's not about diffuse harm, it's about whether anyone was harmed at all besides the accused.
This is precisely the point that is contention. The entire argument for prohibiting marijuana is that this is, in fact, not the case, and that, through a number of indirect channels, people "smoking weed in private" harms others throughout society in a variety of ways.
Obviously, as I said, there is considerable disagreement about whether this is, in fact, the case, (and, also, as to whether, even if it is, prohibition mitigates or exacerbates these harms, and as to whether, in any case, prohibition is an ethically-acceptable response even if the harms exist and prohibition mitigates them.)
But it certainly is not the case that those who support prohibition generally agree that the crimes are "victimless" that those opposed to prohibition describe that way.
Lots of what I would call "victimless crimes" are outlawed because of what the proponents of criminalization see as focused harm. Prostitution, for example, is seen as either harming the prostitute, or harming the patron's family. For drugs, it's often considered that the harm is focused on the user, not diffuse.
And again, lots of crimes with diffuse harm are generally agreed on to not fall into the "victimless" category, like dumping toxic materials.
There is some truth to this for some drugs, but not even close to most.
My point is just that there is no connection, as far as I can see, between crimes which some people as presenting diffuse harm, and crimes which other people see as being victimless. All combinations are not only present but common.
It is rather looking at the overall picture of "What are the consequences of allowing weed to be bought/sold/grown. Is there harm in it?" The whole infrastructure, not just the end user.
>In the other direction, smoking weed in private harms nobody except the smoker. The harm is so focused it doesn't even touch anyone besides the offender. Yet this is almost the canonical example of "victimless crime."
It's true that this doesn't directly harm anyone. However, if the smoker is doing this 'illegally' (without a medical license, not in WA or CO, etc) and didn't grow it, he/she is participating in and supporting an illegal drug market via increased demand. If the smoker weren't participating, it would reduce the demand that drives smugglers and the horrific things in Mexico.