Why are Hindu women not allowed to enter prayer areas like temples while they are menstruating? I want to know that why are they not allowed to worship not asked to be separate from family for three days.
First of all women were not cursed with mensuration, rather the women accepted mensuration as mentioned in the story of taittriya samhita-
He appealed to a concourse of women, 'Take the third of my guilt.' They said, 'Let us choose a boon; let us obtain offspring from after the menses; let us enjoy intercourse at will up to birth.' Therefore women obtain offspring from after the menses, and enjoy intercourse at will up to birth, for that was what they chose as a boon. They took a third of his guilt, it became (a woman) with stained garments; therefore one should not converse with (a woman) with stained garments , one should not sit with her, nor eat her food, for she keeps emitting the colour of guilt. Or rather they say, 'Woman's food is unguent, and there fore one should not accept (from her) unguent, but anything else (can be accepted) at will.'
The son born of intercourse with (a woman) with stained garments is accursed; ...
Now why they are not allowed in temples- mensuration is considered impure as it makes you ritually impure you can't take part in yajnas or worship rituals.
Any kind of waste material- blood, dead body things that are dominant of tamas, rajas makes one ritually impure
Also the fact that women are only considered impure on mensuration days- devala smriti, parashar smriti, and yajnavalkya smriti say that a women if raped or becomes impregnated with a child of maleccha becomes pure again just after her 1 cycle of mensuration are over, so you see mensuration and abstinence for three days provides women with ritual purity for a month, while the same law does not apply to brahmins because they have to do gayatri jaap and sandhyavandanam to keep their ritualistic purity intact everyday.
Women (possess) an unequalled means of purification; they never become (entirely) foul. For month by month their temporary uncleanness removes their sins. (Vashistha Dharmasutra 28.4)
So mensuration has both positive and negative sides, on mensuration days you become ritually impure, but the same mensuration provides women with ritualistic purity for a month.
Btw- Hindu scriptures that deal with myths-sagas-stories do not say to segregate women in temples,
The laws of temple worship are placed by agama shastras, they place different bans.
And laws of yajnas and other Vedic rituals are placed by brahmanas- they place different bans.
The laws of everyday life are placed by smritis.
The story is found in purans which explain the stories and philosophy behind Vedas.
Also mensuration in hinduism is said to be "rajas wala dosh" which means Rajas is higher in women during mensuration period. That is true. As women are emotionally more sensitive during menses.