Re: Why bother keeping Aikido 'pure'?
For me, aiki do is a study of the application of aiki. The kata we find in aikido are derived from the early movements often demonstrated by O Sensei. The intention behind them was to create common vessels in which practitioners could express aiki. There is commonality to sister Japanese arts, especially those arts shared by some of the earlier students who lead the kata curriculum. The kata are a "paint by numbers," approach to helping reduce the stress of manufacturing a proper martial shape when also trying to express aiki. The curriculum of kata we have is kinda a "starter kit" of a larger set of martial movement that exists.
I think that it is difficult to express aiki. I think when you are referring to those who argue about limiting the formal kata of aikido, you are talking about an argument based on a limit of knowledge. To some extent, I can sympathize with this perspective because probably most of what we do is not expressing aiki, so the number of kata that we proclaim to comprehend does not change our inability to express aiki. The converse to that argument is that everything we do is aiki, and there is no limit of knowledge. To some extent, I can sympathize with this argument because that is the intended purpose of our training, to transcend the need for a model that solicits proper aiki movement.
Kata is a tool to help reduce the stress of remember what to do - it creates an outside shape that is reproducible and transferrable. There are some aikido people who will never really move beyond that phase of their training. For those who do, they invigorate their kata with aiki. For those who are good, they move with aiki without a need to put that movement into a outside shape.
This brings us back to shu ha ri training. Aiki is a basic body skill. You can use it for many things, but only if you learn aiki, not a shape that solicits aiki-like movement. The kata in aikido are designed to preserve the movement to express aiki, not fight. If you have built a body of knowledge that lets you expand your kata knowledge and still express aiki, great.