Bacteria are microscopic living organisms, usually one-celled, that can be found everywhere. They can be dangerous, such as when they cause infection, or beneficial, as in the process of fermentation (such as in wine) and that of decomposition. But because it come from our dirty laundry it can be a dangerous thing.
It could be worse if you not clean your washing machine, you washing machine can be smelly. do you realy want to clean your laundry with smelly washing machine?
of course with dirty washing machine we can't clean our laundry as effective as clean washing machine.