I think the best way I can explain my view on this is with a scenario.Found items do add an interesting point to replication. How many props are found items and how many are an amalgamation of found items?
What about original designs using greeblies, like Star Wars?
Let’s say I designed and built some water guns and was selling them for $10. Some guy comes along and buys one, slaps some paint on it and sells it for $15, im probably not going to have much of a problem with it because the original intent of my my work was to make $10 for my self.
Now let’s say same scenario, but instead of charging $10 I’m giving them away for free to everyone in my neighborhood because they all love water gun fights so much. Same guy comes by grabs as many as he likes, slaps some paint on them, and then starts charging people without even telling them where they can get the free water pistol to begin with. As the original creator my original intent (to freely share with everyone) has been capitalized on, something I very much didn’t want. Now there’s two options, start charging per pistol to keep this from happening or stop all together.
This isn’t always the case because some modelers genuinely don’t mind if you use their design to make money. But it does hurt a lot of people. the ones already being paid before hand probably don’t care/mind as much as the people who put it out in the spirit of the community.