Balak lead a group of slavers to Astroid X57 in what was supposed to be a simple slave grab. However, when they got there, he stated his intentions to crash Asteroid X57 into Terra Nova and forced the rest of the slavers to do his bidding by sheer intimidation.
He believes that he must crash Asteroid X57 into Terra Nova in order to get the attention of the rest of the galaxy to the batarian's "plight", which is actually a self-imposed exile caused by colonial conflicts between themselves adn humans. If actions like crashing Asteroid X57 are not done, then the galaxy will never understand the pain the bataraians have had to go though since their exile.
When the player finds Balak; he offers them a choice; either let him go and save a few prisoners he is holding, or fight him and let the prisionsers be blown up by a bomb. If the player chooses to let Balak go, he will activate the bomb anyways, but the player will have a chance to disable it before it goes off. If the player fights and defeats Balak, they can either let him die or arrest him and let an Alliance ship pick him up. No matter what the player does, Balak will end his plot.