The debate over whether natural wood has natural anti-bacterial properties and plastic is a natural petri dish is interesting
Not sure about the debate thing, but in acommercial establishment the health departments embargo wooden cutting boards. It has to do with the ability to clean them properly because of the nicks, slashes, groves placed in them by the knoves as well as the seems present when most of them are made glueing together pieces of wood. It has to due with the degree of cleaning. In a commercial establishment both wood and polypropele cutting board could go through the large commercial dishwashers so that is not the reason.
In terms of dulling a knife, it is my experience professionally that reason most knives get dull is that people neglect to properly hone them when using them. The simple practice of using a diamond laced steel freuqently is the prime reason most knoves are not razor sharp. The average individual sharpens their knife when it dulls rathert han swipe it on a steel.