I don't dislike United fans. A lot of my friends are red. They are however a team that attracts (or attracted) people that have no link to the team or this city at all and think that supporting a successful team makes them special.
I don't even dislike these plastics when I really think about it. I actually feel sorry for them, because however deluded they are, deep down they know they'll never truly have an actual connection to their team and if a lot of them were a bit older they'd be Liverpool fans and a bit younger they'd be City fans. It's actually tragically sad.