If using the work as training data was lawful (which hasn't been always the case as we know today) I tend to agree with you, but it might depend: creating an alteration of the work might be prohibited altogether or you might need to give proper credit to the original authors and that might already be violated when you present certain output to a user. In general, the user is responsible to obey the license of the original work. The problem is that the LLM doed not know on which works its output (mostly) is based on. So in theory, no output for which copyright laws might apply should be used whatsoever.