I find that everyone who recommends solo diving only recommends it if you have as much experience as they do. Funny how everyone thinks it's a bad idea until then, right?
Solo diving isn't smart, period. Looking both ways before running a red light and having years of driving experience makes it less dangerous, but it doesn't make it a smart decision.
I think that's an overly broad statement and a fairly irrelevent analogy.
Solo diving ... like all diving ... is a matter of risk analysis and mitigation. But in order to mitigate the risks, you have to understand what they are, and have the skills and equipment to deal with them. This is no different than any other approach to diving. The most significant difference is that you will not be relying on someone else to help you. As with many recreational activities, the level at which you can be properly prepared to do that far exceeds the basic training you received when first entering that activity.
There are many ways to dive. Whether they're smart or not will depend not just on your skill and experience level, but your comfort zone and the circumstances of the dive. Not every dive should be approached as a solo dive, even by the very experienced solo diver. And some dives will actually be less risky to do solo by the properly prepared solo diver.
There are no straight-forward solutions that apply equally to all divers under all circumstances ... however much people of a certain idealogical persuasion would have us believe that there are. Diving with a buddy also has inherent risks and drawbacks which must be mitigated. Unfortunately, what we see in the typical recreational setting is a bunch of people who have been told they should always dive with a buddy with little or no effort put into training them how to actually do that ... and that leads to problems and complications that will often put a diver at risks that they neither anticipated nor prepared for. We read about those people in the Accidents and Incidents forum almost every day.
Solo diving isn't the preferred solution to that problem ... developing good buddy skills and being choosy about who you dive with are. On the other hand, solo diving can be a valid choice for quite a lot of recreational settings, if the diver puts appropriate levels of experience, training, planning and preparation into the dive.
OW training does not even begin to prepare you for that process. OW training ... even at the best levels ... introduces you to the basics of safe diving practices. It prepares you for diving in relatively benign conditions and introduces you to mitigation practices for the most common problems you might encounter as a new diver ... and it does that with the assumption that you will be diving with a similarly-trained buddy. It does not cover many of the essential skills that a diver must have before they consider diving on their own.
And that is why most solo divers believe that it takes more experience to dive solo. There's nothing funny about it ... it's basic risk mitigation.
... Bob (Grateful Diver)