I actually do (as a slim woman) see my thinness as a privilege, in the sense that I was fortunate enough to be raised slim. Neither of my parents were overweight, my mum was a healthy curvy size 12-14 so not 'thin', and we didn't particularly eat very healthy meals or exercise, but my upbringing meant I was very slim as I wasn't over fed or given tonnes and tonnes of junk.
as an adult now, I've been as low as 9st 7 (I'm 5ft 9) and am currently the heaviest I've ever been at 11st (my BMI is still healthy and I'm around a size 12). I hate it and want to lose weight. I've successfully lost weight before so I know I can do it, but I do think it's a privilege that my default growing up before I had choices over my food intake was to be thin. It's easier I think to be a healthy weight as an adult if that's been your default to go back to, and you have an appropriate relationship with food, than it would be to be raised obese and have to find a whole new way of eating and feeling about food to achieve a body you've never had before, I can't phrase it very well but I hope that makes sense.
If I was raised overweight then I'm already starting off on the wrong foot health wise and in terms of my size, and have to work so much harder to achieve a normal weight. So I do feel privileged that I was raised by parents who ensured my body was a normal healthy size, as it's easier as an adult to maintain it.
I have caught myself thinking uncharitable thoughts about obese people, like 'how did they let themselves get to this point' and 'how can you disrespect your own body to this extent when you are lucky to have a working body' and judgments that day people must be lazy or have no impulse control. I try catch those thoughts and be aware of them but if I have them I don't doubt others do, I know a lot of otherwise nice people who see someone obese and think it's disgusting or embarrassing. It's interesting how the fat positivity movement has grown in recent years to celebrate being morbidly obese, I'm not sure whether that's helpful. But nor is castigating and judging someone for their weight. I don't know if shame is the healthiest motivator.
Of course as an adult it's down to you to have whatever weight you want to have, and I think the constant emphasis on how hard it is to lose weight doesn't help, as it frightens people off from even trying and gives a ready made excuse to just give up. But it's definitely a privilege to have started life a healthy weight. I genuinely believe it's a form of child abuse/neglect to raise children who are obese, setting them up for a lifetime of struggle and health problems.