I put a K&N on my previous bike ('82 Yamaha XJ650RJ), mainly because it was renewable and I was anticipating trouble finding parts for a 27 year old model. K&N claims of better breathing and performance were attractive, too. I'm not convinced the bike ran better.
Two years and about 6000 miles later I started having carb trouble - slow or no return to idle when warm. I was dismayed to find the carb throats and intake side of the slides were completely dark brown from a thin coat of dirt, stuck to the surface by a film of red filter oil. I eventually traced the idle problem to leaky throttle shaft seals, so I cannot say the K&N caused any damage. Nonetheless, I switched back to the stock paper filter.
I suppose it is possible that a standard paper filter passes the same fine dust as a K&N, but without being oiled by the filter, it just passes through the engine. I prefer to think that the paper filter is actually stopping the dirt.
Larry