I said it in another post, I'll say it again here. (lol) If Aikido didn't work as a martial art, it wouldn't exist as a martial art. Everyone who says 'it's good to question your art' are certainly correct, but there's a difference between asking why or how Aikido works and asking IF it works. One is constructive; it helps us to explore the different aspects of Aikido under a variety of situations. The other is not - that kind of doubt is a hindrance in training, as it causes one to think "What's the point if it isn't going to work?"
I'm going to be honest; although one of the reasons I started Aikido was the non-competetive aspect, and decided on Shin-shin Toitsu as one of the softest styles, I do believe that the lack of kumite is a major cause of doubt. We westerners like seeing cause-and-effect; we often need it demonstrated graphically that something works, rather than trusting in the knowledge of those that have gone before.
For myself, I look at Aikido with eyes experienced in tactics and fighting arts. My opinion is that aikido, soft as it is, is a highly potent, effective, powerful Martial Art with a strong spiritual foundation. That is, of course, my own opinion. There are others with equal or greater experience than me who won't agree. To those folks, all I can ask is...
What the heck are you taking it for, then?