I know thin-shaming exists, and this 'only real women have curves' bullshit annoys me, and the DOVE campaign for 'real women' had all overweight and fat women on it, like thin women are not womanly or feminine or attractive. Very rude.
But it's ludicrous to suggest that thin/slim people get such a hard time in life, and as much bullying and goading and insults, as fat/obese people. They simply do not. Fat people are called (and thought of) as less intelligent, stinky, unhygienic, slow, badly educated, and generally unattractive.
When men are looking for a woman on a dating site, they will very rarely go for a woman who is fat. Most men will be looking for thin, slim, athletic, sporty, and occasionally curvy. No man will get mocked by his mates for having a girlfriend/wife who is on the thin side... They will get mocked and ribbed if their girlfriend/wife is rather fat though.
No way in hell do thin/slim people have the same amount of nasty shit aimed at them as overweight/fat people do.
I agree that we used to be thinner for sure. I have recently been watching FRIENDS, and Monica (in 1994,) looked REALLY thin, like bone thin to me. Can't have been more than 7 stone. Yet, 25 years ago, she looked a normal weight and size to me.
Conversely, the 'fat bloke' in The Full Monty film who had the piss taken out of his weight at every available opportunity, did look and appear fat then. Now, 30 years later, he looks fairly standard, and just has what today is classed as a dad-bod.
So we have definitely got bigger as a nation. But we do evolve and progress as a nation, and I feel a size 6 to 8 (and a weight of 7 to 7.5 stone) is not attainable for many women these days. Indeed, I very rarely meet any women over 21, who are below a size 12/below 10 stone. Very slim women (like size 8 or under and below 8 stone,) are very rare.
I am about 10 stone 10, middle aged, and 5 ft 6, and a size 14, so not toooooo big. And I am happy with how I look. I have been up to 13 stone, and down to 9.
The OP does come across as a bit smug though. It's quite hard to lose weight and keep it off. As a pp said, if it was so easy, how come so many people are fat? Do you think people ENJOY being fat? 
As I said, most women I know (over 21,) are on average, between 10 and 11 and a half stone and a size 12 to 14, and they are all slim, fit, sporty, and curvy, and ALL of them are healthy.
Most are NOT a size 6, and they do not weigh 7 stone. Even though many women on mumsnet claim this. 