Interesting debating technique... You're not going to get out of it so easy.

You put forward the argument that it is not effective and I have rebutted it. Now you have to rebutt my rebuttal and put forward another compelling argument.
If you've read my bio, you'll know that I have done several different arts. The training method in each of these arts are slightly different, some of the applications are more overt (like jujitsu and arnis), whilst others are moderately discernable (e.g. karate), and some are mostly obscured by the training method (e.g. aikido and taiji).
Each art is unique, but the brutal applications are both visible and hidden in each, to varying extents. To the casual observer, an art practiced as a choreographed dance, might look ineffectual, but to the discerning eye, the devastatingly and deceptively simple martial applications are there for the taking.... providing that one knows what to look for. IMHE, the ones that look like a dance ritual are usually the more devastatingly brutal ones... e.g. silat.

It's a integral part of many East-Asian arts, where "learning to steal technique" is the de rigeur teaching modality. So, what is shown and demonstrated is quite often the
omote version - i.e. the surface level technique. It is up to the student to discover the
ura of the technique - i.e. what lies hidden just below the surface.
In Japanese culture there is this cultural construct of
soto (outside) vs
uchi (inside). Unless you are immediate family, or Sensei's golden boy, everyone else is
soto - and only insiders are privy to the inner workings of the art.
That is not to say that even though you are an outsider, you would be condemned forever without learning the true art. If you were talented enough, you could probably figure it out yourself. Many have done so quite independently of whatever formal and informal teaching they may have received. This is all part of the "traditional" (and very Zen-like) teaching methods. As I recall, Takeda never showed Ueshiba everything, and likewise, Ueshiba never showed his disciples anything - they all had to work for it.
The sad fact is, many martial artists (not just aikido), are stuck at the outer level stuff - the
omote. And because they are not
uchi deshi (inner circle disciples), they are never shown the
ura - the "real stuff" that makes the techniques work. But every once in while, someone works it out on their own....
So, in answer to your question, what makes me think that aikido is effective? The answer is simple. From all the years of being an outsider, learning to steal technique, I can see the potential of the art and I understand why aikido is practiced the way it is. It is merely a training method for attaining certain body skills - not unlike any other martial art. And from my experience with other martial arts, I can see the parallels, similarities and distinct differences.
In short, it's not the art that's ineffective, but rather the person's relative skill or ability in applying the art. I have sparred with TKD players and karateka, rolled with jujitsuka, pushed hands with taiji players, and duked it out with escrimadors. There's good ones and then there's not so good ones.
But to label an art as ineffective, because the skill level of certain individuals is below your standard, is to ignore the fact that some are simply better than others. Some have better body skills than others, and are better able to utilize them accordingly.
Now it's your turn... you say it's ineffective, now stand by your argument and say why you believe it is so.