A sense of shame isn't properly a virtue—since it belongs really to the body (not the soul) and the passions.
Shame also belongs almost exclusively to the young, since they're always messing up and suffering embarrassment. There should be no call for a mature person to feel shame.
Same thing for a good person. If you're good, you shouldn't be doing wicked things that'll make you feel poorly about yourself.
Aristotle believes that we shouldn't be praised as decent for feeling shame (when we've done something wrong), since being naughty is a voluntarily done bad thing.
And you shouldn't voluntarily choose to do the wrong thing, now should you?
Aristotle points out that self-restraint isn't quite a virtue, either, and promises to discuss this in depth later.