DY & Joseph – +1. Additionally, I am sure that Rav Shach, zatsal, himself thought that Chabad does many good things.
Additionally, we aren’t necessarily even talking about agreeing with Rav Shach but about not saying that he was wrong.
Also, as I pointed out by Rav Avigdor Miller, it’s not a question of whether or not you agree with his conclusions; the issue is that you are saying that he did something wrong by giving a reason for a tragedy.
If Rav Shach, zatsal gave a reason for a tragedy, then you cannot say it is wrong to do so (for someone on Rav Shach’s level).