I think I will jump into this.
I've done it. Once. It wasn't a shade account though. It was on my third, maybe fourth day of play, before I ever subscribed. Me and another n00b at the time saw the Ar-234 and REALLY wanted to try it in the MA. So, I upped a Ju-87, he upped a P-51D. We met up, and he flew straight and level while I tried to shoot him. My aim was so horrible we went at it for about 20-30 minutes without me getting a single kill. So, we decided to switch, I would be the Pony, he would be the Stuka. Again, I flew straight and level, and he was never able to kill me. Finally, we gave up and I've never done it again.
MY personal motivation to do this was this: I was new, and I wanted to fly t3h ub3r jet.
The reasons I've never done it again: 1) It's easier to get bomber perks by bombing things than trying to shoot another guy, even flying straight and level. 2) Maybe its just me, but for some strange reason, I care about what the good guys here think of me. Not guys like Dextur or Axer, but folks like Corky, Widewing, Lusche, etc. I wouldn't want to be shunned by such great people for doing something so dweebish and low. 3) It was boring. The true fun of Aces High is the thrill of the fight. And you don't get that vulching a shade. 4) I realised that was, in a way, (In my oppinion anyway) cheating. And I am not a cheater.
So I tried it, once, to get easy bomber perks. I failed. I never tried it again. So that's my reasoning. However, quite obviously, the same does not apply to these kids.