I think everyone seems to be missing a very interesting point here, that the Buddha actually said that if he were to accept nuns into the order, the Dharma will end 500 years sooner than it would normally end. This is within the scripture itself. The question here is WHY. How would this be possible? Why is it that if women joined the order, it would hasten the demise of Buddhism from our world? That was the reason that the Buddha gave for not ordaining nuns, according to the sutras.
You have a good point here and I think if there is an order of monks and nuns, it would take twice the amount of merits to sustain the teachings. Hence, with less merits to sustain the teachings, the lifespan of the Buddha's teaching to remain on earth had to be shortened as a result. Remember, it takes a tremendous amount of merits to sustain the pure teachings of the Buddha.
There's nothing wrong with a woman having to become ordained but the Buddha made it extra hard for them in preparation of the extra hardship and discrimination they would receive in ancient India, in a society that is biased against women especially in the area of spirituality. Many people often overlook the social circumstances that lead the Buddha to act in this particular manner.
