Quote Originally Posted by Kraggenmor
I.E. The AI will wait longer before backstabbing you.

Since the end result is going to be that I wind up backstabbed regardless, I don't see any reason to spend my time, and my empire's florins, in the hopes that it backstabs me in 40 turns instead of 20.
No, the result will be that within 20 turns you aren't backstabbed by two factions at the same time which will be followed up by another three factions dogpiling on you because your relations and reputation go down.
If you never tried which effect it has, you shouldn't discard it so easily.

You can do without it, but if you don't blitz it's a lot harder if you don't use diplomacy.