In it, the author tells a story of someone in a village in a less developed country who cannot afford pesticides. So he starts a war between two ant colonies in order to drive out the ants that are destroying a beloved fruit tree.
You can do the same thing for gut flora. You don't have to wipe things out first. Trying to wipe the gut clean is extremely hard on the body. It's much easier on the body to just feed the good flora and give them support so they start crowding out things you don't want. It's a gentler path. It just takes persistence.