He wasn't even all that against the broad-strokes idea of invading Equestria, odd as it may have seemed. Equestria in general (and his little sis specifically) had an unbeaten win-loss record against invasions. They were useful, like a vaccine. Kept the citizenry on their hooftips and made sure they practiced their evacuation drills. A nice little war would give his heir some good practical lessons in adapting pre-battle plans into live battlefield strategy.