The complex processes in nature has adopted over millions of years. A particular behaviour in a single species can affect other species through 20 intermediate causations. Every aspect can have many different effects. System properties also has different effects depending on environment and situation. The thing that looks useless can be crucially important in rare circumstances. Seemingly positive changes may have unforeseen consequences years later.
Everything we do to our self and our environment has an effect on the body, psyche, culture and more. The addition of one single food source may indirectly change the expression of a latent gene that had a role in fighting a parasite, coming from floods once in a hundred years, altering the psychological adaptability of the tribe, leading to cultural change involving how other foods are prepared, resulting in infertility. There are some human problems that has increased in industrialized countries the last two hundred years. We often don't know why.
There is a long history of people introducing technology to solve problems without understanding the effect on the environment and ecosystems. The type of complexity might make it impossible to ever learn the effect a certain change will have, even using powerful computer simulations. We should keep and encourage a diversity of living conditions. Especially for those who wants to continue the lifestyle that has been practiced for hundreds of years. We may not know the effect the things we do know will have on us in a thousand years.