You are entitled to your opinion. Since you are probably running an outboard virtually any oil you picked up in an auto parts store while blindfolded would probably be ok for a season. Most of the cheaper engine oils out there are nominally engineered for cars, or spark ignition engines. The same can NOT be said for folks who own inboard engines, particularly diesels.
Diesel compression combustion can release sulphur into the oil which ends up as sulphuric acid that can eat away at the finely engineered moving and stationary parts of an engine. Oils that are made for diesels have additives that help reduce the negative effects of sulphur; oils that are made for gas engines have no such additives.
If you want to prolong the life of your inboard engine then you should understand that not all oils are created equal. If you are running a lawn mower or an outboard then nearly any oil of the right grade will do in a pinch.
If you read Nigel Caulder's "Boatowners Mechanical & Electrical Manual" you would find a few paragraphs devoted to just this subject. Diesel engines require the right oil to extend their working life. Outboard engines are easily replaced. Inboard engines not so much.
