Its one thing to fight for yourself and your own sense of honor. Sure you'd fight with pride but if you lost you'd only have yourself to look to, only yourself as judge and jury. Manny Pacquiao, no matter we ever thought of him, always fought for a nation, always. In many ways Manny Pacquiao was an ambassador of the Philippines, so the antics exhibited by Mayweather would be unthinkable for Pacquiao no matter what his personal moral failings are.
I would imagine he feels so horrible for his fans and countrymen. This is where the burden of fame exacts an unjust price, but the price must be equal to the reward.