This is a big reason why I’m not very involved in horse-related social media pages (outside of here and another forum). There are a lot of people that seem to have a lot to say, none of which is kind or constructive, and more often than not, they don’t seem to be as educated as they want others to perceive them as.
IME, both online and in real life, it seems the ones that are the biggest critics and always trying to make others feel inferior tend to be the ones who don’t know much about what they’re talking about, but desperately want others to think they do. Those who are actually knowledgeable don’t need to criticize others for the sole purpose of making themselves look superior, are not nearly so narrow-minded, and are typically too busy actually riding/training/etc. to obsessively comment on every social media post they see. It’s generally best to take opinions from these types of people with a large grain of salt.
Also, I concur that a lot of people seem so used to obese horses that they see a fit one as skinny, and tend to judge different breeds by the breeds they’re used to.