This may end up being another rant, but;
It appears that we are talking about two separate things here--
1: Fun/competitive games against two people
2: Teaching Games (ShidouGo)
While they overlap, they
are different.
The aim of "1", is for both sides to have an interesting, challenging games. In this case, Handicaps just makes perfect sense.
As for case "2", which has nothing to do with handicap, the aim for the stronger player/Sensei is to 1: create situations (often tailored to the weaker player/Student) Whereby the student's response is inquired, or situations whereby thr student will learn the most, 2: test the Kai, spirit attitude an aptitude of the student.
Technically, handicap stones are not necessary for purpose "2", but to then say they are pointless would be a very narrow statement to make. This is because, one, there is a good aspect to handicap stones, and two...
...Purposes "1" and "2" are often combined...
...Which makes complete sense. Why force yourself to do one or the other when you can do both?
That being said, I personally believe that if a beginner wants to play withoit a hamdicap, they should be allowed to do so. Clearly, purpose "1" does not apply.
Likewise, if a stronger player recommends giving a handicap to a beginner, it good form for the beginner to take one even though he may prefer not to, and even if the stronger player is wrong imposing the handicap-- at least, for the first few games. After a while, it would be hard to refuse you an even game if you had been patiently playing with a handi all that time.
HOWEVER, there are other reasons why a handicap would want to be given apart from purpose "1". For example;
#1,
If you where to play all your teaching games, as a student, without handicap, only your fuseki would be trained well, leaving little room for endgame training.
And if your intention was to drag out a hopeless game to the end, then you mightas well have put a handicap in the first place. It is a bit like, upon being given a handicap, forcefully snatching your opponent's bowl of white stones, to switch it with the black.
#2
Many of the beginners who
insist and insist on playing an even game, are the kind of people who, as children, would beg and beg and make a lot of fluff about wanting a violin/guitar/piano/etc, and, upon receiving the instrument expecting to become the next mozart in 5 minutes, pack it up in three after finding that an oumce of difficulty is invloved of you want to be an expert.
The more
extremely adamant a person is to play without any kind of assistant stones, the more the other players suspect that the person would be discouraged in not having played the divine move itself on their first try.
HOWEVER, there ARE people who prefer not to be given a handicap
all the time, who do not belong to this bracket.
I hope I'm a closer fit to this!
After I had reached the level where I coud defeat Touya Meijin... Err, on the GBA, don't worry... I thought my next challenge would be to defeat GnuGo within Jago client. I usually played without handicap: I prefer it that way. I also liked taking a three or two stone handicap. Why? It had nothing to do with strength difference; it was because it just looked nice. 4, 5, 6, 7, 8, and 9 did not look so aesthetically pleasing, and that was the only reason I never used them.
I personally belive that the healthiest thing to do, no matter what the goals of the idividual are, is to spit it 30:30:30, between full handicap, half-handi, and even games. I thinks it's also a double-purpose move that solved this problem as well. And the other 10%? Be free to experiment with Go, please be free, there are no Go police...
The same applies to board sizes.
Well what about teaching games with pros (assuming you are strangers? Uberdude put it slightly loosely in saying that it might be considered rude, it isn't always the case that they would see it as "rude" in the sense you might first think. It also depends on the pro. Maybe it would be better to something along the lines of "you'd be seen as having a certain questionable trait", but I won't know myself what is correct. A 13 year old 1p wouldn't be the same as a veteran former top pro.
I rembember as a table tennis beginner, asking my gar superior oppenent to keep serving as fast as he could (making it boring for him). He kindly endured

this may be akin to Igo, as many have the perception that you could pick up a bat and whack a ball and say your playing table tennis (your quite clearly not, that is roleplay

)
I know this may sound, as usual, like I'm pretending to an expert or earworthy about a subject in which I'm definitely not. But I hope at least a little confusion would be cleared (if just a little. And there's probably 5% more ranting and clarification which I've forgotten by now, using a 3" without spellchacker

).