haha you guys are so funny fighting over this.  I think we all can agree that macro particles can do damage.  At what point is micro micro?  Dont you people realize the piston and cylinder walls have a sandpaper like surface on the micro scale????  Look at the surface under a electron microscope and it'll look like the rocky mountains.  You cannot get a truly "smooth" surface.  Even on the atomic level there is friction and wear.  Its all relative.  How much sophistication on reduction of wear and friction compared to the cost of manufacturing and maintenance. 

If micro-particles were truly bad then auto engines wouldn't last for 400k miles.  Sure your engine would probably have less wear if you always used fresh oil, but at what cost of resources and maintenance costs? REGARDLESS this is besides the point.  The question that is being debated is is it ok to reuse the "stuff" that comes out of an RC 4 stroke crank vent.  Will it kill your engine?  Outright no.  Could it reduce its life span?  Possible but can you measure by how much?  Is the cost of reduced engine life greater than the cost of extra cleaning supplies, extra time to clean the plane, and possible oil damage to the airframe?  Who knows.... I think one thing we all can agree on is that IF you want to route the vent back into the engine,,,, put a filter on it to get the macro particles out.  Its a personal preference, not the end of the world. 

To the original poster,,, just do what you want and test the results.  If you dont get the results you want try a new configuration.... this how most things are discovered/invented.