Our society often innocently creates and perpetuates stereotypes, but these stereotypes often lead to unfair discrimination and persecution when the stereotype is unfavorable. For example, if we are walking through a park late at night and encounter three senior citizens wearing fur coats and walking with canes, we may not feel as threatened as if we were met by three high school-aged boys wearing leather jackets. Why is this so? We have made a generalization in each case.
People like to insult each other, as for some it is the only way they feel important themselves. I have heard plenty of insults that have lost their original meaning, or are now used in a way that doesn't even make sense. We tend to fall the easiest common denominator when it comes to language.
Though it sounds bad, I believe it is in our nature to condone and perpetuate stereotypes. I grew up believing people who went to church were good and those who rode motorcycles were bad. I know this is not true but I still feel comfortable near church folks and uncomfortable around motorcyclists. Stereotypes don't happen overnight and it takes tremendous and repetitive effort to overcome them. For this reason, I believe we are a society which condones and perpetuates stereotypes.
In addition to the word scrub, there are other words that continue on for generations, even though people don't know what they mean. A ghetto is one example. People use that word to talk about a terrible place, without thinking about all of the people that gave their lives when they were ordered to live in such horrible places.