I have seen both sides... hate for Diet soda because it tastes terrible, and people who feel that drinking "diet" stuff is not really manly. It's not really a new thing either, just think back to when light beer was seen in the same light. It took a ton of sports stars doing commercials and a lot of advertising dollars to convince your average beer drinker that no, drinking light beer does not indicate that you enjoy taking it in from other dudes.
Kinda funny when you think about it, being that now there are a lot of commercials on saying that you actually are unmanly for drinking the wrong light beer. If they tried it 25 years ago or so the response would be "No, you're not manly because you drink light beer at all." (which is even funnier considering that these guys would then go back to chugging their piss-water that is Budweiser).