True, and like most other things, the amount and concentration matters most.
It's a tough one for me. With all the other things going into the environment, a little Dr. Bronners isn't going to make much difference. But that doesn't mean it's ok. When I pass the cows trashing the stream, upstream from where I'm backpacking, and realize I'm going to feel unsafe even splashing my face with stream water the rest of my trip in the "wilderness", I have a hard time thinking it's "bad" to use some soap. Same with irrigation water runoff from all the fields, with fertilizers etc.
It is "bad", but there are so many things going on that are allowed, which are so much worse for the environment, it's hard to care.
Anyway, most of my outdoor showering is done in the desert, usually miles from the nearest stream. Most of the "natural" soaps recommend 200ft from the nearest water.
As usual it's a matter of "ask the little guy to bend over backwards to be clean, but let the major polluters have a bit of a pass". But again...personal choices. I can choose to be part of the problem or not. A little soap out in the middle of desert isn't a huge concern to me.