This is a very individual decision. You, as the child's parent, know your child best, taking into consideration their age, personality and how you feel about them being involved. Research shows there is no difference in sibling rivalry whether they are present at the birth or not.
Some parents are very comfortable with choosing this option. The birth is viewed as a family event, with the older child being part of the family. Including them in the experience is seen as being more preferable, than telling them they are not allowed to be involved. Birth, like death, is seen as a normal life event, and one that children are not excluded from.
Other parents view birth as an adult event, not fit for children. This is often espoused by people who attempt to protect children from basic human functions, with the presumption that they will be better equipped to handle them when older. However, children are not pre-conditioned to have any views on birth, and are only indoctrinated by adults (who themselves may perceive birth as an unpleasant, or a frightening experience). Also be aware that children are exposed to birth and death through the media, animals and their own life experiences, and rarely perceive it as anything but fascinating. They often approach the experience very casually, to everyone's surprise.
Some women choose to exclude their children because they believe they will not able to be to relax in their labour, or they are scheduled for a Caesarean. These are valid reasons but can be worked around, with some thought and preparation if you want to.
Others feel torn between not really wanting their child around while they labour, but feel they cannot be separated from them. This can be a real dilemma for women who have always been the sole carer, and have never had extended periods of separation from their child. This concern in itself could interfere with the woman being able to relax enough to give birth.