My understanding is basically that OPEC is similar to a workers union. Countries band together and set terms that dictate the price and the supply available in the market.

UAE leaving OPEC is like breaking up a workers union. UAE is no longer required to restrict how much oil it exports, and also doesn't have to set a price floor. They're allowed to sell more oil cheaper, potentially at the expense of neighboring OPEC countries.

Which to me sounds like a good thing for the rest of the world?

Ordinarily a Cartel is illegal. If say the US breakfast cereal manufacturers decided to all agree they'll charge a minimum $20 per kilogram, no bulk discounts, the government can and likely will (assuming they don't remember to bribe Donald Trump) prosecute them and force them to stop doing that.

If you've been involved in an SDO ("Standards Development Organisation" think ISO or the IETF although the IETF would insist that they are not in fact an "Organisation" they will admit to being in effect an SDO) you've probably at least glanced at documents explaining that you absolutely must not do anything which looks like Cartel activity, you can't use the SDO to agree prices, or to cut up territory or similar things. The SDO's lawyers will have insisted they make sure every participant knows about this because they don't want to end up in prison or worse.

However the trick for OPEC is that it's a cartel of sovereign entities. It can't be against the rules because its members are the ones who decide the rules. So Chevron and Shell and so on cannot be members of OPEC but the UAE and Venezuela can.

> Which to me sounds like a good thing for the rest of the world?

It probably isn't a bad thing, but let's not overestimate the beneficial effects. The reason oil prices are high right now isn't because of cartel fuckery, it's because of Trump and his war. And oil supply chains are in such chaos because of Trump's war that even if it ended tomorrow it would take markets multiple years to return to a pre-war state.

The bottom line is that oil prices are going to be elevated for years to come, and when oil prices are high, OPEC has nothing to do other than sit back and collect the profits. And thanks to the ongoing solar revolution, oil's days as the world's predominant geopolitical poker chip are numbered; by mid-century OPEC won't be relevant anyway.

That’s similar to unions in general, but of course workers unions was the first thing out of the hat.