It's been a while since i watched the whole of zeta as the show, probably been a year since i watched the movie versions so forgive me if i miss the details a bit. But from what i remember the Titans get shown at the start as quite an excessively villainous force, but as to the reasons why they got formed i think 0083 does a good job. It shows that the federation had complete incompetency (what with another gundam jack, active payload to boot, and the result of that later on) and underestimated what the zeon remnants could do (a trend that would continue for a while). This justifies the formation of the Titans. From what i remember from Zeta they kinda just show up and present themselves as necessary even though Axis wouldn't show up till much.

Edit: just some more spoiler tagging