What was stopping the original artists from producing copies of their work, or even copies of Lichtenstein's? That would have been the rebuttal I would have tried.
But what Lichtenstein did was transform cultural detritus into something considered beautiful and culturally relevant. High art by the people who decide what that is.
Glancing at the artist's [article on Wikipedia](https://en.wikipedia.org/wiki/Roy_Lichtenstein ), it looks like some folks really liked his work and would pay a lot of money for it..? But, why?