If someone feels that their relationship with their teacher can't handle that then they'd be better off not speaking up and taking "sides".
It's not a matter of me taking sides. Or not taking sides. It's very much a matter of the tone of a given discussion. As you said, if point can be made respectfully and politely, the facts on some level can speak for themselves. But leave the "judgements" out of it.
Now this has not happened, so I am being hypothetical, but were one the several people I host at my dojo regularly to post on a public forum that my teacher was a "liar" or directly disparage him by name, do you honestly think I could still be hosting him as if nothing had happened?
There are a number of great folks like Dan who are from outside our community of Aikido practitioners who are generous enough to share what they know with us for little if any return. They take active pleasure in seeing how they can help people be better.
If they want to be able to continue to do that, they need to ease up on their constant public criticism of the art... it drives people away rather than convincing them of anything. I am on record any number of times as saying I don't think that any of these guys understand Aikido. They don't seem to mind that I say so and we are all still buddies. They share with me and I take what I can out of it all. But more people would respond if everything weren't so determinedly negative.
And when you cross into talking about individuals you enter a very dangerous zone. The idea that we should do so while they are alive so that they can respond if they wish is just plain not going to happen. Can you imagine any 8th Dan getting into a give and take about Aikido fact and fiction with anyone publicly much less a non-Aikido person perceived as being disrespectful? Remember what Kensho Furuya's reaction was to the forum? He was so out of here... why folks thought they could talk to him like they talk to their on-line buddies always amazed me.
Well, some of us have important on-going relationships with various teachers. All it would take to seriously queer things up would be for some idiot to send a letter with some quote taken out of context and there'd be hell to pay. I am trying my level best to get doors opened for various people so that the whole community can benefit from their knowledge. But I need and expect a bit of consideration for these efforts in the form of not doing things that make these efforts more difficult or even impossible. There are times when debating certain facts is just indulging, times when nothing positive is there to be gained. Folks do need to understand that.