Where do you stop though mate? Would you be happy if Taylor was the ref for the Chelsea v Everton match? That match directly affects United, as they are directly competing against United for a champions league place. You have to draw the line somewhere. Every ref is going to have a preference. Shoud a ref from Leeds be able to ref United? Should Mike Dean be allowed to ref teams from Manchester.
You just have to hope that the ref's are professional and Taylor has been in his 2 Manchester derbies.
He might have a stinker today, but I do nit think it will be down to any bias.