Brabantio is incensed at the news that his daughter has been consorting with Othello, and even more angry at the idea that the two are to be married. He always looked to Othello as a worthy general and in some ways a worthy servant but he never imagined that he would be so bold as to woo his daughter.
He has accused Othello of using witchcraft and stealing his daughter away but when the suggestion is made that she played a role in the romance, he utters this line. The idea is that he will be willing to accept the consequences of his pronouncements being wrong. If Othello in fact did not bewitch the girl, if she returned his affections and actively pursued him as well, then he says he is willing to accept destruction.
Part of that is his willingness to accept the situation if his daughter in fact chose it, but another aspect of it is his feeling of impending doom if his daughter in fact is going to be married to this Moorish general.