Maybe, maybe not. I don't know. Things change over time anyhow. China can launch a military strike without going through North Korean territory anyways (though it would certainly be convenient to do so). Why do you say that China won't tell North Korea it can rule the South when it's all done? The North would find that tempting, if they trusted the Chinese to uphold it.

I'm surprised you don't turn my "situation may change" comment against me. South Korea may be an enemy tomorrow. That's the biggest counter argument to arming them, and the biggest risk. I don't have a great counter to that line of argument. The only thing I will say is Russia and China are, right now, happily arming our enemies (Pakistan, North Korea, possibly Iran). That's happening no matter what we do.