Still plenty of fans will be upset.
In all seriousness, I actually blame the extended universe for this, both what is now known as legends as well as the new canon. The books, the videogames, etc. A lot of that stuff is fun and exciting, but it also creates a very inconsistent narative and inconsistent rules for the universe. As a result, Star Wars fans have a ton of material to work with to create fan theories, head canon, etc. Which in general, is all well and good, but for some of the more vocal Star Wars fans, they're really attached to some of their views of what the Star Wars universe should look like and how it should operate. So when a new movie comes out, easily the most important Star Wars product there is both in financial terms as well as story telling terms, and it doesn't jive with what they're expecting, the don't like it as much.
I've argued in the past that TFA is just a flawed movie, and I'm fine with that. Some of the more out there arguments against the movie though . . ? I just wanna say "Easy guys. It's just a story."