They do have an identity mate. Its just different to ours, and personally I much prefer ours to theirs. There's is one of a big brother attitude, maybe it stems from them being the older club I don't know. They feel they're superior and we're in their shadow. Ask any genuine pig and that's what they think. Arrogance is not something they're even aware of. They consider themselves one of the biggest clubs in the country and have a proud history.
They totally dismiss us as second fiddle and our history even though if you look through the history of the two clubs neither club has dominated over the other for long. Attendance wise, both clubs have a very similar average attendance fan base. The main difference is for a big game such as at Wembley they attract a larger fan base from their "glory" fan base who only attend such games, whereas, in my view, United have a higher percentage of fans who call themselves Blades that actually attend the games regularly. The Wembley games for them just leads even more to the delusion that they genuinely belong as one of the elite clubs yet the next game they're back to the 22-27000 fans just like we get, as proved by the attendance records this season.
Neither club has ever been consistently at the top like a Man U etc. Essentially both clubs are big clubs but one sees themselves as superior to their actual status.