It is about integrity.
This is a quote from the Shido Yoron where integrity is compared with the joint in a bamboo stem :
"The setsu of the samurai (shisetsu).
When your shiki (samurai ki) is overflowing you should go on to work on your setsu. Setsu is a name which is taken originally from the joints of bamboo; although bamboo has the spirit to grow and pierce the heavens, if it was not for the tightness of the joints it would not be able to endure the frost and the snow, go through all the four seasons and change its colours. If the spirit of the samurai lacks setsu how can he function properly?"
To apply a double standard shows a lack of shisetsu.
Well, Saito Setsudo (Shido Yoron) was another late Tokugawa Confucian scholar who had some romantic ideas about the samurai - without ever having really experienced battle. Like Nitobe, he also turned towards the West later on. There's nothing wrong with his ideas, some of them are quite nice, but I wouldn't take them as standard practice for the samurai class in Japan.
Going back to the original post - I'll agree that double standards are not usually a nice idea, does anyone really disagree with that? But of course, since people may disagree about whether double standards are being applied or not, without a specific example the question is kind of meaningless...