thanks for getting back on the subject under discussion. My understanding is that to be tarred is to be identified and marked as an undesireable, anti-social or just a plain criminal. The mob usually uses a brush to apply the tar (like a paint brush). A person who is "tarred with the same brush" is a person (I think) who is accused of being connected to an unpopular act committed by another person. At least, this is my understanding. I guess that it is somehow connected with tarring and feathering.