Let me answer by analogy.

When western Europeans showed up in the New World, they brought alcohol with them. Suddenly large percentages of the Native Americans were alcoholics.

We know now that some people carry genes that process alcohol better than other people. We also know (and have known) that people who never drink never become alcoholics. Furthermore, we know that when an addictive substance is introduced to a organism there is a point past which the organism will continue to consume the substance at the expense of personal well-being, including up to death. That is, chronic physical addiction.

These people were acting in an unchanged manner -- a normal manner -- but their environment changed.

Should we have berated the Native Americans for being so susceptible to alcohol? Use societal and moral pressure to tell them what lousy choices they have made? Were the NA that lived before alcohol introduction "better" (well) than those who lived after it who were addicted (sick)?

Before we knew about the dosing thing, were those people sick? Or now that we know that a the amount of lifetime exposure that triggers alcoholism in NAs is much less than others, could we call any particular experience with alcohol a bad decision? If I need 4 beers to become an alcoholic, and you need 40 thousand, yet neither of us know which number we have, is going out for a beer in college something society should tell us is bad?

These are complex issues for which simple words that have thousands of years of baggage behind them like "disease" aren't going to work. My opinion is that if the individual makes decisions that he/she knows with greater than a 50% certainty will cause eventual long-term bodily harm, then the consequences are not a disease -- it's a personal choice. Even though it may have attributes of a disease. But I don't think the rising number of obese people is due to a huge number of people making informed choices with probable negative consequence. You eat a few high-carb meals in your teens and now subconsciously you are craving an insulin fix that makes you overeat. I eat a hundred times more high carb meals and I do not have the same condition. When we went out for fish and chips at 21, were either of us committing some sort of purposeful act to get fat? I don't think so, yet one of us now has a lifelong condition. So without any change in our behavior, environmental conditions contribute to changing the way our bodies and minds work. So yes, these people are sick -- in some sense of the word. (forgive the over-broad use of the carb model here. It is incidental to the argument)

However society "dumbing down" illnesses to be everything from shyness to immaturity is also not going to work, because "illness" has this huge social stigma: you are broken, we have an obligation to fix you. Sorry, but I don't need to be fixed for everything I have that you might find as an illness. Some of these things I might enjoy, and some of these things I might feel a personal need to struggle with as a way of understanding the human condition. And I object at people telling me that I "should" do something or another in order to conform to some ever-tightening standard of normality. In addition, I am beginning to suspect that the eventual result here is a homogenized population -- an idea I find so abhorrent that I would rather give up medicine altogether as a species. (I understand this is a radical position) So in that sense, the word "sick" is not correct at all.