I think one of the unsung morals in SMT IV Apocalypse is the danger of placing all your hopes or entire worth into another person. What might be called a parasocial relationship.
The Real Flynn is by no means self-centered or hostile since he does very much care for the people of Tokyo. All the same though, while good and necessary that he revived their hopes in IV's neutral route, his celebrity status posed a problem as people began investing all their hopes and expectations in him. That when he was kidnapped by Krishna, it immediately led to defeated anguish and fearful uncertainty. It also motivated some Hunters to take action, but there was nonetheless a permeating sense of doubt and loss of direction.
Flynn inspiring hope in the hearts of Tokyo was never meant to rally people around him as their one and only savior, but to encourage them to take charge in their own lives for a better tomorrow. Nonetheless though, the former was what ultimately happened. And I think it was that loss of a savior and the desperation to have him back that made Tokyo so especially vulnerable to Shesha Flynn's manipulation.
What especially stands out to me is during Armageddon at Camp Ichigaya when "Flynn" rallies his Hunters to recklessly charge at Merkabah and Lucifer, essentially throwing their lives away out of thoughtless, blind trust. Nanashi can try to stop them, but it just angers the Hunters and gets him accused of protecting their enemies. The Hunters are not thinking for themselves whatsoever.
IVA stresses throughout the game the importance of thinking for ourselves and making our own decisions. There are many who fall victim to blindly following the angels or demons. And there are also far too many who blindly follow Flynn as their sole savior, which the Divine Powers took advantage of.
A recurring theme in IVA is possession and I would think this to be an extension of that. IVA cautions us not to deeply invest in someone at the cost of our own needs or independence. Whether that person is a celebrity, a politician, a friend, a relative, or anyone else. Even if that person isn't actually taking advantage of us, the one sided'ness and worshipping in any relationship is all the same still unhealthy and dangerous.
