Raquel...

Resistance to weight loss doesn't just happen with going on and off induction ala Atkins. It happens with ANY diet where you repeatedly gain, then try to lose weight. Every time you gain and then try to lose, your body becomes more resistant to losing again. Years of low calorie dieting have much the same effect; your metabolism is reset to survive on a lower level of calories which makes weight gain very easy and weight loss very difficult. This is a built-in defense against periods of famine. A "healthy" body should not lose it's ability to lose excess fat, but after years of low calorie dieting and abuse, most people no longer have "healthy" bodies in that sense. An occasional indescretion is not a reason to go back to induction levels again. Dr. Atkins recognizes that we are all human and prone to the occasional slip and addresses that in his book. Personally, after 16 months on low carb, I have very little difficulty sticking with it and am rarely tempted to eat something I shouldn't.
We can "survive" on any food available to us, true enough, but that doesn't mean we will survive in a healthy state. Yes, we are omnivorous and that's not a fact that is incompatable with low carbing. I eat meat, vegetables, fats, some fruits, nuts and berries. I avoid sugar, flour and any highly processed or refined foods.
As far as too much meat or protein diminishing thyroid function, define "too much". I really don't eat much more protein than I did before low carb (if I'm actually eating more at all). I just cut out all the other high carb junk I was eating with it. I've also had my thyroid function tested twice since I started and it's been normal both times.
I agree that many people are going to and do miss the foods that they have enjoyed for decades, but isn't it "enjoyment" of those very foods that brought them to the land of obesity in the first place? Is it a flaw of the diet that many crave those foods and sometimes binge on them or a flaw in metabolic order caused by eating those foods and then a human lack of willpower?