Don't a lot of people in France look at you badly if you only speak English? I read that this is especially true in more "proud French areas" like Paris etc.
Yes and no. It was still there in the late 90's and early aughts. That said Parisians just don't like anyone not from Paris. They look down on other French people not from Paris. When you're from Paris, then you'll be judged on your arrondissement. Basically, Paris is a really judgy place but the rest of the country isn't. This isn't all that different from other countries' major cities (NYC, London, etc).
That said, you'll get by, meet a lot of nice people from all over, get to vacation regularly in places which are "once in a lifetime travels" for most Americans, etc.
Clearly not in start up environments. What do bother some shopkeepers or restaurants owners for example, is when tourists speak english to them very fast and naturally assuming everybody speaks english. But then if you ask first politely "i'm sorry i don't speak french", then you'll only receive warm welcomes.