Imagine that Yogg-sarron's corruption of the watchers is like the fight with their help. If he didn't corrupt them, word would have gotten out about him being there. 2 things could happen here: A quick phone call to algalon saying how there is a reckless Old God and BOOM!, or they go down to his cell to fight him with your help and take him down easily enough. If all Four of them aren't there to help, then the fight gets fairly difficult.

My theory is that the Old Gods serve Azeroth as it's master. Since most, if not all, of the Old God names come from Lovecraft, whats to keep Azeroth itself from being an Old God. That could be why they can't destroy ALL the Old Gods without destroying Azeroth.

That's what I'm saying. He didn't corrupt the Keepers with the intention of calling down Algalon; calling down Algalon was, ironically, his failsafe. If the forces of the Alliance and Horde (the players) managed to break his hold on the Keepers and subdue him, then they would be confronted with Algalon and thus defeat him, furthering Yogg-Saron's plans.

Xanatos Gambit indeed.

That's a fairly risky Xanatos Gambit, though. While I do agree with the idea that he corrupted the Watchers to further the end of spreading chaos and madness, I'm unsure that deliberately summoning Algalon would be a good idea.

Because if we weren't powerful enough, well, he'd be dead. Sure, we'd be dead too, but that'd be small consolation to an ancient being that considers us little more than insects. He couldn't have even used the corrupted Watchers to combat Algalon if we failed, as to open the door, as we would have already fought them and broken them from his grasp to get the key.

I think Yogg was confident enough that he was more powerful than Algalon, seeing as the Titans couldn't even fully imprison him, so players who could defeat him could defeat Algalon. Of course game mechanics proved otherwise, but lorewise I think Yogg thought he had it all planned out.

That is true, but Loken died before we entered into Ulduar. So there was a chance that somehow we'd be able to defeat the Watchers, but die to either him or Algalon.

Then again, it already happened the other way, so I suppose I'm wasting my time with "what if."

Not wasting your time. It's fun to speculate. Lost has been over for months and I still think about it on a near daily basis.

Mmm well we've never actually see how old gods interact? Perhaps they actually really really hate each other or perhaps Yoggy would actually be willing to sacrifice himself for the good of the remaining old gods. I know old gods are suppose to be all old and mysterious but sometimes to leaves a lot of questions.