Some of the generals were not retired and participated in that war. I think that gives them a better right than it does us who weren't there to try and offer insight.
I believe they earned the right to express their opinions, whether or not we agree with them.
I don't think anyone disputes their RIGHT to speak, just their judgement - and reason(s). If one is ticked because hiis pet project was cancelled, and another is pushing a book, that should also be mentioned.