On hakama, isn't it strange that O-Sensei actually required everybody to wear hakama in his dojo, from zero to whatever level.
got this from aikidofaq.com
Mitsugi Saotome Sensei, "The Principles Of Aikido" :"When I was uchi deshi to O Sensei, everyone was required to wear a hakama for practice, beginning with the first time they stepped on the mat. There were no restrictions on the type of hakama you could wear then, so the dojo was a very colorful place. One saw hakama of all sorts, all colors and all qualities, from kendo hakama, to the striped hakama used in Japanese dance, to the costly silk hakama called sendai-hira. I imagine that some beginning student caught the devil for borrowing his grandfather's expensive hakama, meant to be worn only for special occasions and ceremonies, and wearing out its knees in suwariwaza practice."
The reason that it's ok for students below sho-dan to not use hakama was because of it's scarcity, back in pre-war Japan. It was intended to be a temporary policy to avoid expenses.
Some philosophy behind hakama :
"They symbolize the seven virtues of budo," O Sensei said. "These are jin (benevolence), gi (honor or justice), rei (courtesy and etiquette), chi (wisdom, intelligence), shin (sincerity), chu (loyalty), and koh (piety). We find these qualities in the distinguished samurai of the past. The hakama prompts us to reflect on the nature of true bushido. Wearing it symbolizes traditions that have been passed down to us from generation to generation. Aikido is born of the bushido spirit of Japan, and in our practice we must strive to polish the seven traditional virtues."