One of the stronger factors influencing the frequency of wars is the ratio of young men to older men. Life extension would change that ratio to imply fewer wars. See http://earthops.org/immigration/Mesquida_Wiener99.pdf.
Stable regimes seem to have less need for oppression than unstable ones. So while I see some risk that mild oppression will be more common with life extension, I find it hard to see how that would increase existential risks.
But why do young men cause wars (assuming they do)? If everyone remains biologically 22 forever, are they psychologically more similar to actual 22 year-olds or to whatever their chronological age is? If younger men are more aggressive due to higher testosterone levels (or whatever) agelessness might actually have the opposite effect, increasing the percentage of the male population which is aggressive.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.