A person can make their own choice by reading up on it. Noting ASTM tests and information available on the internet....or they can play jr. scientist and watch oil drain from a hole in a cup. Up to the open minded individual.
"conventional 5W-30 motor oil is a petroleum-based oil that is thick at low temperatures and thin at high temperatures. To change this variance, oil manufacturers use additives to change the oil's properties, reducing its viscosity at lower temperatures and thickening the oil at higher temperatures. When it's freshly made, conventional 5W-30 motor oil acts like its synthetic counterpart, but over time, the chemical additives break down or vaporize, returning the oil to its original consistency.
By contrast, synthetic oils are designed to match a specific type of multi-grade oil from the beginning. Even without additives, a synthetic 5W-30 motor oil will not degrade or change viscosity–it may only become slightly thicker from contaminants."
Hearst Auto Research, Car and Driver Publications.
