I like Pip and Kyphis's comments. While I understand that for training folks, Skilldamage hurts, I'm reminded of a discussion months ago here about enforcing rules about the Sparring grounds (I think). What I got out of that discussion was to simply ask politely, rather than Flame-rant against the people "breaking the rule" there.
For myself, Eon's been kind enough to smack my defenses around for skill damage, yes, but then silently fed me some wins to balance it out while I idled. I say this not to gloat, but to offer an alternative, and acceptance of the skill. He earned it, and should be able to use it as he feels fit. But Staying online and public doesn't necessarily extrapolate to "OMG I'll have no stats left".
It would be interested to see a specific ritual or creature ability to counter this, if balanced properly, but such a simple solution would probably result in everyone defending with such things, and make the possible "training defenses" much more shallow in strategy. Those with more combat-brains could probably flesh out the idea better, but my gut reaction is that outright cancelling it with some ability would be a bad thing. (no offense to the suggestion itself, merely explaining my thoughts).