Monarchies are not rewarded to people based on merit, they are rewarded based on blood and tradition..When you think about it the fact that Aiko's father is the heir and well the new little prince's father isn't the heir isn't necessarily "fair" to begin with. They have exactly the same blood. Even though from what I've read the IHA and the current emperor would perfer the second son. But tradition is tradition. No matter how anyone feels about that one, surely people can agree that the best royal isn't necessarily the oldest. One only has to look at Queen Elizabeth II"s father and uncle to see that one clearly. Then, there's the fact that the monarchy isn't open to everyone!
So since the monarch is based on Tradition and blood, if the tradition has alwasy been that the monarchy is based on through the male line. I don't see what the big deal is. Maybe its discriminatory, but the the fact that the possibility of being Emperor someday isn't open to everyone is discriminatory as well!
For 1500 years of Tradition. The Japanese monarchy has been based on the male line. That's been their tradition and it is an unbroken line. Then, there is the factor that the Monarch isn't just the head of state in Japan. The monarch is also the High Priest of the Shinto religion, and he use to be regarded as a god! I hear that some Japanese quitely still view the emperor as a god (the more traditional ones.) So, it means that you have a situation which is certainly tense at best, and certainly something that shouldn't be messed with by Westernors but should only be dealt with by the Japanese people anyways.
My feelings are that it would be one thing to change the rule while there was no young boy who was an heir. But now that there is this young boy. It seems kind of unfair to take away what is now his birth right (out from under him) According to the Consitution, 1500 years of Tradition. This young boy's father is legally entitled to be the Crown Prince's heir, and this young boy his father's heir. It's unfair to the Crown Princess brother and to the little guy for this role to be changed. In my book, nothing really is being "stolen" from Aiko because she never had the right to become Empress in the first place. Besides why would she want that job?
In the end what makes people keep monarchies is the traditional/history aspect. When you just "do a way with Tradition left and right, it may make people say hey why do we need a monarchy after all
