I find my visceral response to this question intriguing. As a 'mostly thin, sorta fit' person, my inclination was to immediate think this would devolve into a fattie-apologism thread.
I'm pleasantly surprised to see that it hasn't. A few comments towards us 'skinnies' but it has been pretty fair.
A few thoughts.
I definitely know some 'skinny-flabbies' who have low body weight yet are markedly out of shape. However, they still have the advantage of carrying low weight - much lower stress on joints, heart, etc. I think it would be easier for them to get into shape (whatever that means) than an obese person. Complete speculation on my part.
The idea that you can be obese/overweight (not sure we made the distinction here) and be completely healthy is somewhat a fallacy. There are also papers on the other side of the debate, and where the argument falls down is on cardiovascular health. Abdominal obesity IS a risk factor regardless of blood pressure, cholesterol, and other markers. Also, cancer incidence is definitely higher in overweight folk. Again, not sure what the definition of overweight is and whether that means a person is generally large or has abdominal obesity.
What does that mean in the context of this discussion? Nothing, except that regardless of our starting point we'd all benefit from exercise and working on being fit, and we can't wish ourselves something we aren't.