If one is sure of the coins they have whether they are pure or tainted, they can avoid using mixers.
It is not about that, it is not always about the source of the coin, you are almost insinuating here that mixers should only be common for people into illicit businesses, but that is not true.
In as much as i do not mix frequently, another person may have their reason for mixing frequently, i don't mean using multiple mixers, i mean using one mixer, but often, their funds don't have to be from illicit dealings for them to do that.
I understand your points, mixers are actually meant to keep anonymity of some business transactions, it shouldn't be interpreted that mixers are for ilisit business transactions because there are people who may want to send money from person to another for legitimate business but wouldn't like it to be exposed to the general public.
Again, anything that involves sending huge sum of money from one person to another requires some privacy, even sending local faits currencies from one individual to others involves some certain degree of anonymity.
I personally think that sending money for businesses should be done without people knowing, whether sending locally or intentionally, or to individuals. I like doing business and even sending money to friends with maximum anonymity, home or abroad.