Except the genocide of the beastman races would be incredibly unethical? Like the Mamool Ja, Qiqurn, and Goblins seem to be by in large on friendly terms with Eorzea (Though they can't step foot in Ul'dah). There are pockets of Beastmen who are quite reasonable and fine folks as well, and there's a lot of evidence to suggest if Limsa Lominsa would stop breaking the treaties they had with the Kobolds, they probably wouldn't have a reason to summon Titan. Keep in mind the Garleans kind of want to stamp out religion all together.. In Eorzea.. The place that all huddled around in prayer in hopes that the Twelve would save them from Dalamud. That's not gonna fly with the Garleans.

There's a ton of issues with Eorzea allying with Garlemald, Eorzea should never do it.