Would you still be cool with Sergio if he accepted a Pacquiao fight even after saying he there was no way he would fight him due to the size mismatch? Would you lose some respect for him for going for the little guy after what he said? Obviously only on the off chance that it does happen, which it won't. As long as he isn't the one begging for it like Williams, I think it should be fine.
Why would you hold it against him? If he gets an opportunity like that he'd be crazy not to jump all over it. He'd make more in one night than he probably has his entire career and the opportunity to set his name in boxing history.