GB, we are eating up the GTVA propaganda because we have no UEF propaganda. Also, what we know from the prose provides a good reason for the war.
1. The GTVA needed the economic and industrial might of Sol in order to bolster their economy to prevent collapse. If the economy of the GTVA collapses, then they can't muster the necessary firepower needed to stop the third Shivan invasion. If that happens, then all the Terrans and Vasudans in the GTVA die, and Sol is left all alone for the Shivans to destroy whenever they feel like.
2. The GTVA feared mass immigration to Sol from the outer colonies, which would leave them unmanned and unprotected when the inevitable third Shivan incursion would come.
3. The Council of Elders are, to be blunt, naive, considering they first thought the GTVA was as enlightened as them, as well as their insistence on diplomatic talks with a clearly hostile GTVA even after the destruction of several UEF frigates and an assault on Neptune.
4. The Ubuntu philosophy could easily be considered pacifistic, which is a death sentence in a galaxy where Terrans and Vasudans are surrounded on all sides by a genocidal alien race with limitless numbers and ships far more powerful than anything Terrans and Vasudans can build in comparable numbers. (At least 80 Sathanes against a single Colossus that took 20 years and a fortune to build.) In a situation like that, a strong and well-supported military is essential to survival, and it looks like the UEF military does not have much backing, at least at the start of the Sol-GTVA War. I doubt the Terran-Vasudan military would receive much backing if Ubuntu took over the GTVA, leading to fatal weakness when the Shivans return.
GB, I would love it if you could provide me with reasons to consider backing the UEF in this war, because so far, from my reading of the prose, it seems like the GTVA needs to win this war as it is the only thing standing between Terrans and Vasudans and a painful death by Shivan beam fire.