Usually Hindu temples are places of worship with a difference. Meanwhile unlike other religions, every Hindu deity has a history to tell and even the same deity in different places may be worshipped in a different manner. Furthermore the story of a deity needs to be understood first before even worshipping that deity and that is why not everyone needs to worship every deity but if one wants to worship a deity, one need to essentially follow the rules of worship.
Since Hindus have innumerous deities that no one Hindu person may even know, it is important to understand the deity and the rules of worship before we even attempt to discuss certain customs. Furthermore there is a light chance that women below 10 and more than 50 may also have a chance of menstruation bleeding and this is what is presented during the court arguments as well. Further it is important to understand that this age bar was placed by the kerala Govt. by an ordinance and even the respondents of the sabarimala PIL feel it was arbitrary and it should have been based on procreation ability of women.
Moreover women have a natural monthly cycle of downward flow of blood out of their body, which is the natural process of eliminating the old blood and refilling their body with fresh blood. Hence if this natural process is disrupted by forcing their energy upwards, their downward menstruating flow will disrupt. Apparently the spiritual energy in the temple is so much that normal women will not be able to endure it. Since one needs to visit the temple every year for 18 years, repeatedly practicing Brahmacharya they may lose their potency permanently.