Of course, banning lead in those countries will have a beneficial effect, but I don't think it will quell much unrest. The middle east was unstable well before the introduction of leaded gasoline. And as you said, car ownership isn't as common there.
I think the question of whether lead is a contributing factor in a seemingly endless cycle of violence is one worth answering.
There are so many ....
> Keep in mind that the number of vehicles per capita is much lower in Iraq and Yemen
Certainly that's a datum to take into account (I'm not being sarcastic).
> Your comment ... speaks to a mindset where complicated geopolitical problems can be solved or explained by a simple hack.
Does it now?
Getting these countries to stop burning leaded gasoline sounds like a fairly hard problem to me, just from the fact that they keep doing it. A sibling poster mentions how many problems have had simple solutions, like vitamin C for scurvy, which is true in the abstract but they all took quite a lot of fighting to implement.
Now, I doubt that lead is a significant factor here. But even if it were and it could be demonstrated, would it really be "simple"?
Keep in mind that the number of vehicles per capita is much lower in Iraq and Yemen (the only two countries you mention) than in the United States.
Your comment rubs me the wrong way since it speaks to a mindset where complicated geopolitical problems can be solved or explained by a simple hack. Don't use lead! Peace treaties to follow.