I think the reason a prequel would disturb some people, is because: Watchmen was not like an episodic comic book where the continuing story was devised one-month to the next, but a social commentary built in the structure of an enclosed universe of a single novel; thus the backgrounds of all the characters were only devised to give the greatest effect to that political content, making a prequel (presumably for entertainment value only, but even if not) would be seen as missing the entire point of the graphic novel, therefore any such effort would be undertaken by people who did not fully understand the source material. I had not even known of this prequel till reading about it here and cannot say these are my feelings (but I suppose if I were to really get emotionally attached and think about it they might be) but rather my attempt to explain a possible reason for the behavior of some that seems to perplex you.