[chongli]

If one person writes nonfree software and another person voluntarily uses it, I don't think anything "wrong" has transpired.

Beware the fallacy of composition. What may be "right" in a transaction between individuals can be "wrong" over the entire population. One example of this is the mob effect: if one person takes the time to disagree with you it is not a problem. If thousands of people send you messages of disagreement it becomes an unbearable burden.

Likewise for software. One person using nonfree software made by another person is not much of a problem. When thousands of people use the same nonfree software it becomes a problem due to lock-in, network effects, etc.

[gmluke]

> Beware the fallacy of composition. What may be "right" in a transaction between individuals can be "wrong" over the entire population.

I think this issue is philosophically contentious, and interesting. Even if you don't accept that premise, I wouldn't describe this as a fallacy.

I think fallacy is best used to describe a logical non-sequitur/invalid conclusion. It's independent of whether we agree on the assumptions.

Premise 1: Socrates is a man. Premise 2: All men are mortal. Invalid conclusion: Therefore Pigs can fly.