A very good email from a student of these things:

Dear Jonah,
Did I hear you give serious thought about a ’stability’ argument in favour of the continued Syrian occupation of Lebanon, and against the democratic aspirations of the Lebanese people? I thought you guys were rubbishing anyone pushing the same argument in Iraq!
Syria has always enjoyed playing the role of the arsonist and the fire department. The reason why Hezbollah did not disarm 15 years ago along with all the other militias in Lebanon, as stipulated in the Taef agreement that ended the war in Lebanon, is because the Syrians had other plans for it.
The question that answers your question is why does Hezbollah cling on to Syria’s presence in Lebanon if it is in their favour that Syria withdraws?
In political terms, Hezbollah will be on a much shorter leash after the Syrian withdrawal. This is because a fully sovereign Lebanese government that is accountable to the people and not to its Syrian masters won’t tolerate reckless behaviour from Hezbollah that will be only bring destruction to Lebanon (Notice what is happening with Mahmoud Abbas and the Palestinian terror groups).
And in military terms, Hezbollah won’t be the 800 pound gorilla. It is no match for the Lebanese army. And in fact, it is Syria that is stopping the Lebanese army from deploying in the south of the country, against the wishes of the international community, and against the Lebanese government obligation under UN Resolution 425 that Israel has complied with.
Hezbollah knows that irrespective of the deal they cut now with the opposition, their days will be numbered once the last Syrian soldier has left Lebanon, and that those pledging now to protect the ‘resistance’ after the Syrian withdrawal, will be asking the ‘resistance’ to get real and get with it once the Syrians are out. That is why Hezbollah won’t be cutting a deal with the opposition until it sees that the Syrian withdrawal has become inevitable.

Me: I think I was pretty clear that my gut says that the stability argument is unpersuasive to me, but that I hadn’t heard a forceful case directly on that point.

I should also say — responding to some other emails on this whole thing — my main reservation is not Israel. I think if this instability makes things worse for Israel in the short or medium term, that’s perfectly acceptable. My main question was about Lebanon itself. If Syria leaves does Hezbollah run Lebanon and would that mean replacing one non-democratic ruling system for another? From what people are telling me, the answer is no. The “People Power” movement (I much prefer “Cedar Revolution” by the way) is not looking to replace one dictatorial regime with another. And if that’s the case, great. Bring on the creative destruction.