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.

Breakfast cereal has substitutes so it would be unprofitable to do that. But the meaning behind what you're saying was clear nonetheless.