There is reason to suppose that ingredients in laundry detergents other than surfactants harm the environment more than surfactants do. There is no reason to suppose that most of the ingredients in laundry detergents not advertised as ecologically friendly harm the environment significantly. Laundry detergents that are advertised as ecologically friendly contain much lower amounts of surfactants, on average, than do other laundry detergents. Laundry detergents advertised as environmentally friendly are typically less effective than other detergents, so that larger amounts must be used.
All laundry detergents contain surfactants, which can harm aquatic life. However, the environmental effects of most ingredients in laundry detergents, including most of those in so-called "ecologically friendly" detergents, are unknown. Ttherefore, there is no reason to suppose that laundry detergents advertised as ecologically friendly are less damaging to the environment than other laundry detergents are.
Which one of the following, if true, most weakens the argument?