Well, the fact it has four legs, a brain a fraction of the size (most of which is alloted to olfactory sense, as opposed to ours which has the bulk alloted to vision), the fact that they adapt to limb / sensory loss more readily than we do, the fact that they don't experience self identity at the same level, the fact they don't experience emotion or pain the same way we do, the fact that they don't 'care' the way we do.... Dogs see the world completely differently than we do, and to try to apply human standards to them is an injustice. For instance, for a dog, vision is as secondary as smell is to us. Just because they are different does not make them inferior, or 'just' dogs, but to try to humanize them implies they are inferior.
As far as ignorance, I am quite fluent in dog behavior, the way and why they think and learn how they do, why they react to different stimuli the way they do, and it is by no means as complicated as many would like to think. I've studied their behavior, physiology, and learning capacity for many years. How about you? They are far simpler, and as such, far more adaptable than most give them credit for. Complexity is not always a good thing.
As far as 'guilt', I would feel far guiltier putting a dog through something like the say, the strain of chemo or radiation therapy to treat cancer than I would if I euthanized him humanely. Why? Because the dog doesn't know why he's suddenly sick, wracked with pain, and hairless and itchy. He just knows he is. Yet people will spend thousands doing this to a dog. I simply believe, better to let it take it's course, and when the dog is obviously no longer enjoying life, take him to the vet and release him from it.
To force an animal to linger or deal with the pain of unnecessary surgery and recovery (note: Unecessary) is not doing anything for the dog... it is assuaging your guilt, and protecting you as the human from having to make an even more difficult, if more humane, choice. We put our animals through pain and extended suffering claiming we care and our being humane, when often times it is far more humane to end the pain all together... To believe we are doing the right thing by extending the misery and pain of an animal or putting it 'under the knife' for serious non-life saving surgery because we are somehow helping it, is where the ignorance lies IMHO.
It's 'needs' are quite different from yours.