Re: How can Aikido teach you discipline if you love it?
I don't know too much about discipline, since I myself am lacking quite significantly in that regard. But then again, that's why I train, to improve myself, so I suppose the only people who thinks they have enough discipline, must be the ones who lack it the most. Since you are aware of the existence of the problem, that automatically puts you ahead of the crowd, as you are addressing it at all times, which helps tremendously.
From what I've been taught by my own sensei, discipline isn't really anything other than that, having the knowledge that you are fallible and undisciplined, and then making a conscious effort to address it at any and every opportunity. Recognizing that you are taking the easy way out or avoiding difficulty is the first step. After that, it's just pushing yourself to do it, regardless of whether you like it or hate it (the kata training you had in mind).
Thing is, like most things in life, discipline isn't binary, but on a sliding scale. You are not either undisciplined or disciplined, but rather just getting more and more able to control yourself. The mind drives the body. In that case, the more experience you have in life, and the more difficulties you've overcome, the better you will be at telling yourself to keep going no matter what. There's a big difference between being able to make every training session that you are physically able to, and continue to perform a demonstration after having your arm broken. Training in Japan is so important because of that. Many Japanese Aikidokas demonstrates their determination and discipline, sometimes almost to extremes, so by observing them train, you can get an idea of how they view discipline, and what it means to attain it.
My sensei summarized it in one sweet japanese saying: do, not do not.