The raindrops do not fall upward. (Ask a Vorlon question, get a Vorlon answer.)
Remember how the Vorlons went nuts after Kosh died and Sheridan opened up the "unexpected door" by attacking Z'ha'dum? It's been broadly hinted by JMS that Kosh was a stabilizing influence, keeping them under control. Also remember that no Vorlon has died in a very long time. Combine the loss of their sanity check with attempted murder, and they go a little nuts.
It bothered me at the time too, until I remembered that our perception of the Vorlons as wise, albiet reserved and maddenly cryptic, comes from Kosh alone. The others are a little psychotic. At least, that's how I've always read it.