This isn't a problem. All this does is change when their people get happy. On the peaceful setting your people like it when you found a new colony, when you make a trade agreement, and things like that. Bloodthirsty races only enjoy war and killing. Making the AI aggressive but with a peaceful happiness type is perfectly reasonable if it will be spending more time expanding than fighting. Especially since the combat rewards for happiness only apply to the planets in the system where combat occurs.
The problem is only the name. Peaceful should be renamed "Civilization/expansion," Bloodthirsty should be renamed "warrior," and neutral should be renamed, "Does nothing ever." <-- That was sarcasm.
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