I think it is interesting that Jesus asked “WHY is it that thou beholdest the mote that is in thy brother’s eye, but considerest not the beam that is in thine own eye?”   It kind of shows how silly it is to notice someone else’s faults instead of one’s own.  I think Jesus implies that the proper response should be to allow our notice of others’ faults act as an indicator to us that the very same ones exist in us.  (As the saying goes, “It takes one to know one.”)  I don’t think this is meant just to quell fault-finding with others, but also as a call to repentance of the “beam” issues. 

We usually don’t have an idea of how our bad behavior makes others feel, so to see someone else acting the same way and to suffer from it can be a helpful call to repentance.