Would they be content with people using their characters in ads to sell things without receiving anything? I think it's more about the content creator losing control over what the thing they made is being used for, than them explicitly losing money.
My litmus test is, "What Would Bill Watterson do?"
If an artist takes a one-time commission to paint a Calvin & Hobbes frame on a nursery wall, great. If it's on a million t-shirts or Hobbes is selling medical insurance, then that is something different.
The former comes out of appreciation, the latter, pure exploitation.
