Can you understand something without knowing what it is?
You can have knowledge in several different ways. You can have experiential knowledge without having the mental knowledge or understanding. You don't have to understand the physics of thermodynamics in order to know that boiling water is hot, for example. Your body can simply learn from the physical aspects of the art.
I think we're looking at the word "DO" differently. You seem to be looking at it as a literal 'way'. The way I see it, nearly all the techniques found in 'DO' styles came from older styles. These techniques have the same purpose they did when they were made, to injure or restrain someone. I don't see how a technique can be taken from a fighting style and then somehow have it's purposed changed to create peace.
Correct, they did take the techniques from older styles. Why did they change an effective/lethal technique to something other than that?
Politics? possibly, but I contend that politics alone is not enough to sustain long term interest. The people studying the system would have to realize some benefit from the art. What possible benefit can you get out of a "watered" down/"gentrified" system?
Look at the mission statement or philosophical intent the founders very clearly wrote. Gichin Funakoshi was very clear about why he created Karate, as well as Kano, and Uesheba. How can you really argue with what their intent of creating the system was?? May not be why you study it, but it is the intent behind the art.
I've never seen them spar. I've never seen them do anything with a resisting opponent
I have. Heres a little vignette. I was four weeks out of Ranger School and four years of studying a very tough hard core karate. My karate instructor sent me to Saotome Sensei's dojo in DC when I moved there with the Army. After doing the usual "hardcore" beginner thing...you know tryng to really understand the art, but growing impatient with all the senior students that I was convinced could not defend their way out of a paper bag. I baited a 3rd Dan who was well respected in the dojo to play my "what if" boxing, trapped in the corner, can't irimi scenario. (I am a pretty decent boxer, and was in decent shape fresh out of Ranger Training, 6 foot 1, 210 lbs). I pulled the short punches and "checked" him if he tried to irimi. He couldn't do anything with me.
About that time Saotome Sensei walks down the steps from the house into the dojo, so the 3rd Dan says, "lets ask sensei". After a few minutes of Sensei trying to define my "what if" he got in the corner against the wall and say "go ahead". I figured, hey this is a shihan, he should be able to hold his own so I did not hold back and proceed to come in with good jabs and body blows. It took about a split second for him to slip past me somehow and flatten my face against the wall. he is...what....about 4 11, maybe 140lbs??? he held me there while he explained to the 3rd Dan about the problems with paradigms and something about the wall being your friend and not the enemy. I was pretty humbled, and had a sore nose for a few days.
I am now careful when I ask for proof from shihans like Saotome sensei, and Ikeda sensei cause you might get what you ask for.
As far as the culture thing.
Culture may be important to some, that is fine with me. However, I think the training methodolgy is what is important. You can gain the same pschyological, mental, and spiritual benefits out of wrestling, BJJ, Sambo, and even Modern Army Combatives that you can from aikido. It really is what the individual connects with.
One thing I do think you have to be careful with in aikido is the false sense of culture or spirituality that you percieve you gain from the japanese culture that many dojos emulate. It is fine to wear a hakama, it is fine to have a kamiza, and bow and all that, but that ritual is a reminder, it does not make you better, more refined, or more spiritual than any other art like BJJ that simply goes on the mat and trains hard.