Aikido practice is fundamentally about transforming our fearful natures into something else. It is about attaining an internal balance, both mental and physical which allows one to let the world in rather than hold it away. The more one relaxes, the more one can develop that internal balance, the more the stresses of the world simply pass through one without taking hold, without causing damage, and without creating that need to push back which causes so much pain and destruction in our world.
I think this section of George's post is well worth repeating. It is quite important to the topic I think and is worth taking the time to really understand what is being said.
Having said that - How does one transform a fearful nature into something else through Aikido practice exactly? Fear is often only removed through deep understanding of what is feared and why it is feared which in a very real way gives one a degree of POWER over that fear. Fears are also often products of environment and circumstance, developed well over time. For example, if one has consistently lived in an environment where the threat of death or injury by an armed assault is very high, then that fear will be very deep seated and require a very high degree of understanding (iow POWER) to be overcome. The only other option is to become fully unattached to whatever may be lost by the threat that is feared, but attaining skill in non-attachment may be better found in a school of Zen or similar, not a martial art.
As per George's statement, fear creates tension and becomes a block to attaining true balance, so it can be said that as long as fear is a factor in what drives us it will be very difficult to relax and "let the world in." We can only honestly let the world in if we feel secure enough to do so, or if we are totally unattached to any negative effects of "letting the world in."
Part of the reason that the "effectiveness" question comes up regularly is because of fear and attachment. Many simply don't believe that their training methodology (and this includes any training method, not only Aikido) empowers them enough to remove their basic fears towards conflict and confrontation. If this basic fear cannot be removed then the hope of transforming the fearful self into something else is quite slim via that methodology.
So what George is saying is very important to many who train Aikido in its original intent as Budo. If ones practice does not assist one in removing fears through empowerment or unattachment, then what is one really learning to achieve?
Just some thoughts on the subject. I always smile at the effectiveness questions by newbies to the forum because it reminds me of the human-ness of those out there who practice in many different countries, who live in many different realities that may not be appreciated by many. Even Ueshiba M. started his training because of fear. Fortunately he was able to remove enough fear that he started getting to the "good stuff." But I wonder if he did not find empowerment or unattachment if he would have ever achieved what he did to create Aikido after all of it.