Why are evangelical American Christians so fragile and easily offended?

Because they don't have a religion to guide them or a belief in God to support them. Instead, they have substituted a political agenda that they are willing to compromise on, on a moment's notice to secure their superficial desires.

Because they've been taught to take an ancient book of legends and fireside speculations more literally than the dictionary on pain of infinite flaming death by boiling acid cannibalism. Just my opinion.

Challenging someone's core beliefs activates the same fight or flight reaction as physically threatening them.

Fewer people are joining their club. They worry.

because their religion is outwardly directed, they can feel that it's all a show

you just leave them alone, mister

It’s their thing.