For some birthing women, having an attendant at their birth is a comfort to them and helps them feel empowered. While others may feel that having an attendant makes them nervous and uneasy. For these women, having an unassisted birth would be a safer choice.
In order to let natural birth unfold on its own, the mother must be completely surrendered to the process. Some women feel that having a birth attendant helps take away the distraction of being aware of potential anomalies during the birth process so that they can be more focused and centered on the task at hand. For them, an attendant that they trust is an asset to normal birth and not a liability.
Other birthing women believe that having anyone attend them would interfere with their birth process. They might feel nervous about the attendant making suggestions which they might not agree with but wouldn't have the presence of mind to ignore in the moment. Or they might feel that they are being judged on their performance and not able to fully let go and do what feels comfortable for them. There are many other reasons why some birthing women are not comfortable having a birth attendant other than their family or friends and some would even feel safest birthing alone.
The process of normal birth is dependent on the mother feeling safe and supported. Therefore, she must do what she feels most comfortable with. Having an attendant is not a requirement of having an normal birth.
Birth belongs to the mother and her baby. No one should ever take the power away from the mother and tell her where or how to birth her baby. The process of birth is a very sacred event and the decisions of where, how, and with whom to share that event are the mother's to make.