It's a difficult subject and I understand your concerns phoenix - so I'll try to word this carefully as I do NOT want to imply that driving insulin usage low at all costs is the aim.
Type 1 diabetics have the option of trying to balance out anything they eat with insulin. At one extreme someone could eat huge amounts of carbohydrates - say 1000g per day - and theoretically balance that out perfectly with huge amounts of insulin to get "good control". At the other extreme someone could eat zero-carb and do large quantities of low-intensity exercise to drive their insulin usage as low as possible, and also get "good control". And of course in the middle is a sliding scale of carbohydrate to insulin intake, and at all levels of carb intake it's possible to balance it out with insulin to get a good HbA1c (it tends to be harder to get good control with large intakes of carb, but it's possible and let's assume for now this isn't an issue).
These approaches might result in the same blood glucose control, but they're not equivalent at all.
In non-type-1-diabetics (or should I say "anyone who still produces insulin"), if they produce too much insulin (hyperinsulinemia) it's a real problem. It's a causal factor in many health issues - including type 2 diabetes, heart disease, raised blood pressure, obesity, hyperthyroidism and all sorts of other conditions; it's increasingly being linked to various cancers for example. Insulin is an extremely potent hormone, and too much of it is dangerous, just as too little of it is dangerous. As with everything, the body needs the correct balance.
A type 1 diabetic eating lots of carbohydrate and injecting lots of insulin is equivalent to a non-diabetic eating lots of carbohydrate and producing lots of insulin. If natural insulin in too-large quantities is damaging to the non-diabetic, why would injected insulin in too-large quantities NOT be damaging to the diabetic? Type 1 diabetics aren't immune to the problems of elevated insulin levels - T1's can develop insulin resistance, and they can suffer from all of the metabolic disorders that non-diabetics or type 2 diabetics can suffer from.
Type 1's have an added problem. Because the healthy pancreas is so accurate and can fine-tune insulin secretions really quickly, it can release exactly the right amount of insulin. Type 1's inject insulin in large doses, and it tends to take more insulin delivered in this fashion compared to what the pancreas would produce (in the same way that pump users generally use less insulin than someone on MDI, because the doses are smaller and more frequent; so too the pump user still uses more insulin than a pancreas would support because even the best pump delivers insulin far less often than the pancreas). So T1's are already at a disadvantage in that we typically inject more insulin than we'd produce if our pancreases worked.
This is where I at least am coming from (and I think fergus and others are saying the same). The amount of insulin you use does have an effect, and needs to be borne in mind. All other things being equal, it's better to use less insulin than more. But the important part there is "all other things being equal". By this I mean, first and foremost, that T1's absolutely need to take their insulin and keep good control of their HbA1C's - that's just a given, and no way am I suggesting otherwise. Beyond that, there's the fact that people need to have a life and enjoy it - so whatever dietary and exercise regime you decide on has to be one that works for YOU. For the best diabetic control I believe this would involve a low-carb diet and a goodly amount of exercise; but if that makes someone miserable or they know they won't stick with it, then the advantages clearly aren't worth the downsides. It's all a balancing act like everything in life, and I think people just need to be aware of the upsides AND the downsides so they can choose the best path for themselves.
T1's absolutely need their insulin, it's not the devil and I'm extremely grateful that I can inject the stuff and keep on living! For ANY type 1 diabetic my advice would most certainly be to inject the amount you need to get good control - don't reduce dosages and run higher blood sugars just so you can use less insulin. But at the same time, it's a powerful drug and too much of it is harmful, so if someone uses a lot of insulin it's worth thinking about options that might let them reduce that amount while still keeping good control.
