[quote=Flamelord]
Well, Ba'al interpreted it as chastisement. That's just how things happen. Besides, conquering the entirety of the multiverse is too much of a hassle, especially compared to just a galaxy spanning empire. Closest he'd get is wishing to be an Ascended being more powerful than both the Ancients and the Ori, but I don't think we've settled on whether the Ancients can Planeswalk at all (if they care enough to do so)
[/quote]

It's mostly that Sorin sees Ba'al as the exact type to go "WHY STOP AT CONQUERING ONE PLANE (evil laugh)" upon realizing the truth of the Multiverse. Though Sorin doesn't see him as a true threat, he'd be an easy problem to nip in the bud. 

The Elder Dragon he mentioned way back when poses basically the exact same threat, with the difference of being far more powerful than Sorin, and being somewhere unknown in a very big Multiverse. Just a matter of convenience in the end, I suppose.