> in a way that invalidates work of his former team
But if the problems are real, then it is good to point out those problems. You cannot just ignore problems, because it hurts people's feelings.
If people are doing bad things, that cause problems, then yes their work should be invalidated, on the basis of the problems that they cause.
If you do bad things, then yes you should feel bad about the bad things that you did. Because bad things are bad, and you should feel bad about them.
And you are letting everyone else down, if you refuse to condemn bad things that are happening.
You absolutely should feel bad about doing bad things, and you should feel like you let everyone else down, because you did those bad things.
> without hurting morale of the organizations.
If you hurt other people, and do bad things, then you absolutely should feel bad and you absolutely should have your morale hurt. Because you did a bad thing. It is good for you to feel bad about doing bad things.
And if you don't then you are letting everyone else down.