world prices of oil is fairly stable barring war/invasion of oil producing countries

I'm no economic historian, but the data seems to say otherwise.

Oil prices from 1861 until today have always been volatile and easily affected by world events. Hell, you don't need major wars or conflicts for oil prices to fluctuate wildly; it's pure supply and demand.

But here's the thing.

Prior to the formation of OPEC in 1960, the average year-on-year (YOY) variation in oil prices was about 20%, with a maximum change of 143% in 1862. After the formation of OPEC, the average YOY variation up to 2013 remained about the same at 21%, despite the maximum change and actual price being much much higher than before (252% max change due to Vietnam in 1974).

That is the effect that OPEC has on oil prices. While the price and the impact of wars etc on that price is higher due to how mechanized our world is today, the degree of change in that price is still close to historical norms as possible. That's stability, and when you can count on a rough average of 20% over the course of a few years in your cost calculations, you can safely mark up your price by that much because you know you will make up for any loss greater than that over the long term.

If a country does more bad than good ... isnt that the same as doing no good for the world at large?

No, it isn't.

It's pretty well-established that the colonial British basically exploited us and our natural resources for Dear Old Blighty. However, that doesn't change the fact that they did bring quite a lot of modern infrastructure and development to our nation that we certainly benefited from following independence. The latter is something good that they did for us, and that doesn't change even if they also did some pretty nasty and manipulative things to us at the same time.

Same thing applies to the Saudi situation. Regardless of whether they are directly responsible for the deaths of Yemeni civilians or whatever, that doesn't change that they have also helped others. The benefit that 1 Saudi Riyal did isn't erased by the pain caused by the other 2 Saudi Riyals.

Your kind of thinking is the same kind of demonisation that you criticise the Saudis of promoting against Israel. If you think the latter is bad, perhaps you should reevaluate the acceptability of your "Whatever good they did is erased by the bad" attitude.