Quick to judge. That was one of many qualities that Scully had noticed about Agent John Doggett. He seemed to think that he, rather than she - Mulder's partner going on eight years - really knew him and how he thought and behaved.
Just because he had known Mulder years ago, it did not in any way mean that he was right.
In fact, Scully could not be convinced more that Doggett really did not know Mulder at all. Maybe he had once but people change. Mulder had surely changed. It was human nature.
Of course, Mulder had not changed much in the time she'd known him. He was still adamant in his search for the truth. He was Mulder. That's what he did. But maybe he'd been different when John had known him.
Scully had spent the past eight years getting to know Mulder and to think that someone would deny her that was downright infuriating. John Doggett had certainly done that and more.
No matter what she might think of Doggett, though, Scully was certain that he wouldn't give up easily. Given that, it couldn't hurt to have him on the case.
She'd ignore his arrogant nature if it meant finding Mulder.