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.