Group Pride is a good thing, but Group Shame is a good thing too.
There are at least three reasons:
1) It is maturing. Only children think only well of themselves. A group that only expresses pride is essentially a group of children.
2) If one expresses group pride, one is morally obligated to express group shame.
3) If only one group is expected to express shame (and does for past and present actions), then only this group is expected to be governed by rules of morality. It is very interesting of whom expressions of shame are expected.
It means more is morally expected of this group than of anyone else.
And other groups are not expected to act morally, and they do not. One cultural in particular where the relative absence of expressions of shame over the atrocities committed in its name daily is an example of a childish culture lacking in morality and maturity.