How do you decide when to apply this kind of thinking?
For example, if you believe I'm making poor use of my car and you think you could do more good with it, does that make it OK to steal it, on the basis that humanity still has the same number of cars and now one of them is being used more effectively?
I'm not saying it's wrong to pick a dollar up off the floor, just that I'm not convinced the reason it is OK is the reason you gave. I think the reason it is OK to pick a dollar up off the floor is because that dollar basically belongs to nobody at that point.
Casey Neistat has a good video on this topic: The Ethics of Stealing a Bike ( https://www.youtube.com/watch?v=wW6gGyfxn1U ) where he argues that it's never OK to steal someone's bike, but it is OK to steal "nobody's bike", i.e. a bike that has clearly been abandoned.
I think that one should be skeptical of one's own rationalizations for something like that, and also consider all of the costs to everyone. Even if a law is unjust, the machinery that enforces it is going to use resources when the law is flouted. Even if there was no enforcement, any precautions against theft are going to have a cost. Lack of trust has profound effects indirectly.
So what are the costs?
The cost to society of someone picking up a dollar bill is the energy expended in the action. I'd estimate 0.2 calories,[1] and about 3/4 of a cent per calorie,[2] which means about 0.15 cents total.
The cost to society of nobody picking up a dollar bill is the cost of printing a new one, about 7.7 cents.[3]
So I guess picking it up is about 50 times better, and given the moral principle that one should do what everyone should do, or vice versa, therefore I would.
[1]Stretching is about 150 calories per half hour; sitting is about 40 calories per half hour; 110 calories per half hour is 0.2 calories over ~3 seconds. (https://www.livestrong.com/article/438404-does-stretching-bu...)
[2] Americans spend $10-20 per day on food; 2000 calories is a reasonable amount (although Americans average substantially more). (https://www.ers.usda.gov/data-products/ag-and-food-statistic...)
[3]https://www.google.com/search?q=cost+of+printing+a+dollar+bi...