"(a) We call you to be a people of manners, principles, honour, and purity; to reject the immoral acts of fornication, homosexuality, intoxicants, gambling's, and trading with interest."

This is already an incredibly regressive thing to say as a polite request, but in case you weren't aware the "or else" was that his global terror organization would continue to murder innocent civilians.

No, there is no "or else", you are plainly making it up. As I've said, this is the exhortation part of the letter and it's not listed among the reasons for the attacks. Regressive, certainly. Brought as a justification for terrorism, no.