I've been reading "The Crusades: The Authoritative History of the War For the Holy Land" by Thomas Asbridge and it's got me thinking.
Raynald of Châtillon's violent raids are often cited as the reason Near-Eastern Islam would invade the Kingdom of Jerusalem. But from what I've read about Saladin, it seems to me like invasion would be the logical end goal of his ambitions.
Saladin derived a lot of his legitimacy to rule his vast realm by taking up the mantle as "mujahideen" from his ex-liege (and the person to unite the realm previous) Nur Al-din. Jerusalem is considered a holy site for Islam that was invaded by infidels. So the justification for his rule would be the reconquest of the city.
And anyway, the lands of the Kingdom of Jerusalem were valuable for trade with the Med, and would strengthen the connection between Ayyubid Egypt and Syria.
Wouldn't it be in Saladin's best interests to eventually conquer the Kingdom of Jerusalem, even without a figure like Raynald?
I've written about Raynald before, hopefully this helps answer your question as well:
In short, yes, Saladin would have invaded and conquered Jerusalem anyway; Raynald's actions were a convenient excuse for him to do it in 1187. Raynald has traditionally been seen as sort of a "rogue state" acting on his own against royal policy, but more recently, his career has been re-evaluated (by Bernard Hamilton, among others).