system
Given the following post, respond as if you're commenting on Reddit:
human
[Dune] Why did Paul's "terrible purpose" and Leto's "golden path" end up in a jihad? Why did a jihad need to happen?

Paul mentions the Bene Gesserit wanted this to happen, to ensure the survival of the species, which Leto also mentions as the reason for the Scattering.

What about the jihad ensures the survival of the species?
gpt
Alright, first and foremost you have to understand the world that Paul was born into.  The population had been tightly controlled by the existing feudal system and Bene Gesserit programs.  The population was constrained to the planets they already lived on and were generally satisfied with their lives.

That sounds wonderful on face, very little conflict, minimal strife and everyone is satisfied.  Unfortunately, that is the path to stagnation and eventual death.  The genetic controls positioned people to be completely controlled, the social satisfaction stifled innovation and the religion prevented people from reaching their potential.  In short, mankind is on a long slow path to stagnation and death.

Alright, so now we have the world without Paul and his Heirs, so we can talk about what is involved in the golden path.

Leto saw where mankind was headed and realized that the only path to the survival of the species was to fracture them and spread them throughout the universe.  Unfortunately, stagnation and satisfaction was the enemy, so drastic actions were needed.  The golden path showed the way to restart human ingenuity and restart our drive to spread and succeed.  The first step in that path was to clamp down on society through total central control.

That's where the jihad comes in.  Leto's Fremen went force to impose Leto's order and control upon the known galaxy.  They abolished the old feudal system by force and imposed a dictatorship.  The CHOAM and Lanstraad were abolished and the voices of the people and Noble houses were silenced.  The jihad was needed to impose that level of control and authority via force.

The goal was to suppress the population so totally and completely that they would rebel and reject all controls in the future.  At the same time the Fremen and jihad broke the chains in the tightly controlled genetic programs.  The combination was intended to restart human ingenuity and the need to expand and thrive.

From there things get pretty complicated and there is a lot going on behind the scenes, but the jihad was a necessary first step to force the population to once again start thinking for themselves and push them away from stagnation and into expansion once again.