There's a lot of debate on what is considered victimless. Yes, if you don't wear your seatbelt for example, the only one possible hurt is you. Not making your child wear a seatbelt is different. The child is a victim if an accident occurs.
Urination and defecation in public by many is considered a victimless crime, but unsanitary conditions promote the spread of disease. There just isn't an immediately identifiable victim.
Now here is one I agree with: There is a state law against U-turns anywhere. I can see that one as victimless. Unless you cause an accident and kill someone else because you made a U-turn at the top of a blind hill. But there are remedies for that, no U-turn signs.
I see part of the problem is defining what is victimless.
The child seatbelt issue is a good point, and I think ultimately though it comes down to whether or not an injured party ends arising.
The main issue with the myriad of ridiculous laws that cops enforce is that it gives the state the power to decide certain things you may or may not do, under the guise of public safety and preventive measures, even if the only person you may be harming is yourself, as you stated with the seatbelt thing. And because of this beauracracy what usually ends up happening is nonviolent people are apprehended in very violent ways, and are now deemed criminal by the state because of preemptive policing that may or may not actually prevent a crime. Not to mention the ridiculousness of making us pay with taxes to house nonviolent people in prison, if they end up there.
I think things like public urination or defecation could still easily be addressed in a free society with strict private property rights as a violation of private property. Ultimately though it would be up to the property owner as to how they'd choose to deal with that.
Just some food for thought!