Perhaps I was not clear enough. Inclusion which mess with the grit (meaning make hone inconsistent throughout its honing surface) If they are finer and softer than the hone itself that is not that big problem. However when it becomes problem is when they are of lower grit or harder than hone itself. Their "toxicity " comes to play when they mess up (spoil) the work you trying to do for example make deep scratches, rip your edge. This often can be sand inclusions and others.