Just reading a label of a detergent ought to be enough to tell you whether or not you want those chemicals in your soil.
Soaps are made of materials found in nature, fats and lye, which are biodegradeable. Detergents are synthetic (although some of the ingredients are natural); they were developed during World War II when oils to make soap were scarce. Surfactants are used to "cut" grease and control foaming, but are bad for the environment.
There is little doubt that soap is better for your health and the environment than detergents. Detergents are very toxic to fish and wildlife.
Interestingly enough, I got out a box of Tide to look at the ingredients, they weren't listed. I went to their site and they weren't to be found. I certainly want to know what I'm using next to my skin and putting in the septic tank, but they're not going to tell me. :O
There are laundry soap recipes made with pure soap flakes, Ivory, and a few other ingredients that are biodegradeable and safe. They don't always perform as well with hard water, which is why detergents use surfactants and other ingredients, to keep that grayish look from happening to laundry.
----------------------
Life goes on within you and without you - George Harrison