Why is it that blatant ism and ageism are allowed in the presidential race if it is being said by a liberal?

Barack Obama was quoted as saying "You can put lipstick on a pig. It's still a pig. You can wrap an old fish in a piece of paper called change." Yet any negative comment about Obama is banned or attacked, even if it is a legitimate concern. Why is there a double standard, where liberals are allowed to blatantly discriminate?