[pinko]

This is the key point many people miss.

Assuming a basic level of sanitation, less faecal contamination (there is never zero) + less bacterial competition may be worse in practice than more faecal contamination + more bacterial competition.

The key advance in urban human sanitation, as I understand it, was not the use of surfectants so much as getting the open sewers off of the streets.

But I am not an expert on such things. I'd be grateful to be corrected by anyone who is.