As I understand it, the breaking down of body fat to fuel the body causes ketones and high blood sugar, which becomes a vicious cycle, which also causes dehydration and exhaustion and, eventually: DKA. The body can use ketones (and the brain likes them), but to quote our eminent endo consultant: "Ketones plus continued high blood sugar = DKA." And it's not pretty to watch your child hooked up to drips and monitors in intensive care for 72 hours. The idea that someone with T1 could exercise takes me aback, remembering how my son was exhausted for weeks, during which time he hardly got out of bed, and he was then barely able to walk or even stay awake from total exhaustion on the actual day of his diagnosis. For me, that throws out a substantive part of the "thought experiment" argument. Also exercise does not always cause blood sugar to fall - it can have the opposite effect.
So I think you're right that insulin only facilitates the uptake of glucose in body cells. Don't forget though that this is part of a chain reaction which in turn means that glucose doesn't fly wholesale into the bloodstream. When glucose does all diffuse into the blood, it causes cell hunger and the breakdown of more and more body fats to fuel these starving cells; to no avail, as this just produces - more sugar that can't be utilised. However, that's a pretty essential function for someone who has no insulin of their own, particularly when you consider that the body is a system and one action causes another reaction.
As I understand it, before exogenous insulin existed, people "treated" T1 with starvation - the only treatment at that time. I also believe that the end result was invariably the same: death.
Unless someone has a completely unique physiology (which might in fact question a diagnosis of T1), my challenge would be that today, in 2017, all people who have a firm T1D diagnosis, and who produce no insulin of their own, need exogenous insulin to survive.
In my view, when we challenge what we think we know, we are possibly challenging opinion. Also in my view, to challenge that insulin is not necessarily needed to treat T1D, in people who produce none of their own (or not enough), is challenging what I consider to be a proven fact. I hope that's not seen as offensive, but I feel quite strongly that this point needs to be made, having seen the effects of no insulin first hand and being told that my child might actually die, at diagnosis point. I would regret not posting this if one person decided to try some risky "alternative" (for themselves or their child) and ended up making themselves ill or worse.
While we all wish for miracles in relation to this condition (I so desperately do), we also need to face into the realities of where medical science and treatment are today.