PADI say nothing of the sort.
What they do say is that the Open Water course 'qualifies divers to dive independantly, without professional supervision, to a maximum recommended depth of 18m/60ft'.
They also recommend that divers should recieve a 'local orientation' when diving in new and unfamiliar conditions. An orientation can vary between an informal verbal briefing, a guided dive or a formal 'Discover Local Diving' course.
There are two ways to assess the requirement for divemasters...
1) That divers should accept significant limitations in their capability and always ensure their safety by hiring an underwater babysitter.
2) That divers should ensure they recieve high quality training, that actually provides them with the skills, experience, knowledge and mindset to dive safely without reliance upon a professional (which is what PADI intend).
Babysitter or Good Training?
It's actually quite normal in many parts of the world to not have a divemaster. In most parts of the USA, Canada and Europe, divers will rarely have a divemaster guiding dives for them. Whilst the water conditions are typically much more demanding than tropical waters, newly qualified divers are expected to look out for themselves. Typically, divers just book spaces on charter boats, which are not much more than diver-orientated water taxis to the dive sites. No DM, no supervision - although the boat captain will typically provide the information that you need so that you can safely plan and prepare for your dive.
What causes problems? The lack of a divemaster.... or the unnecessary reliance on divemasters in the first place, that allows divers to become negligent in properly developing and maintaining their skills or adopting a more self-reliant, responsible attitude towards their diving?