I remember some people at the time saying TPM (and AOTC) needed to be "darker". Which George immediately pounced on and did his infamous "they're for kids" reply.
"Darker" is kind of a vague term; George interpreted it as "like The Terminator". But I think what people meant by that was, we need more fleshed-out villiains. We need to give them more screen time and actual motivations. And yes, we need to actually see them doing some bad, "dark" things if they are to be truly vilified.