...he has rank:

"...but she had prejudices on the side of ancestry: she had a value for rank and consequence, which blinded her a little to the faults of those who possessed them." (ch 2)

You have to believe that if Wentworth was the second son of an earl, or had been knighted, that her objections would not have been so strong. She might have been blinded a bit to his faults. Perhaps not so much that she would have approved the marriage - there were other objections, of course - but perhaps she wouldn't have been so vehement or her dislike of Wentworth wouldn't have been so strong.