It is also your responsibility to know the divers you are taking. How can you plan a dive if you don't know that? How can you know which divers you should be paying more attention to? How can you anticipate problems?
Most resorts I have been to have a schedule of what dive sites they are doing, and list them on a board for people to sign up on. The people working there are all to happy to tell you a little about the sites before you sign up. This is especially true of wrecks or popular reef dives that have been written about in dive magazines.
The only time I have seen the dives change on board was in Cozumel, the group I had travelled with booked the entire boat, and we decided to dive a different site than the boat was planning to take us to.
In most cases I am sure if you request specific conditions you will be able to be accomodated. It may be with a large resort that has the resources to handle large eclectic groups of divers, or you may have to book a small dive op who is willing to cater to 1 or a few divers all looking to do the same thing.
If we take Belize for example, there are shallow reefs, deeper reefs, and of course the Great Blue Hole. If a new diver fresh out of the pool decides to sign up for the Blue Hole, hoping he can hang at 60 feet, what is the DM to do? The dive goes to about 130 to see the rock formations. Sheould the DM turn the boat around? Force the diver to stay on board while everyone else dives? Force all the other divers to stay at 60 feet looking at nothing for the newb?
No, the dive in the Blue Hole is to 130 feet, where the formations are. There is no law prohibiting an OW diver of any experience level from making that dive, so it is up to the individual to dive, or not to dive, not the DM. They are not breaking any laws.
In an ideal world nobody would have to face those situations. But we don't live in an ideal world, we live in a world full of wonder, surprise, variability, and all that means you have decisions to make.
And I would hate to see the formation of a Scuba Police to make law and enforce it. If you find yourself over your head, don't dive. If you choose to dive and something goes wrong, you have no one to blame but yourself.