The Youtube comments section is particularly nasty. I don't know what it is, but people use that space to say the most toxic things that come to mind. I don't know why this is a thing. If you don't want these comments, disable them on the video or make it private.
*Some* horse people are exactly as you describe them. In fact there is a rather popular horse youtube channel where the owner basically rants and blasts people in 98% of his very long videos. Sometimes he has a point, most of the time he is just yelling in a long video. There is a guitar channel owned by a professional session guitarist that is almost exactly the same as far as the yelling trolling long videos calling everyone idiots.
Maybe it isn't really that *horse people* are elitist jerks that are going to find fault with everything you do, but some of those people are into horses.
You are going to get some of that in any hobby, especially one that involves so many parts and so much knowledge. For example a lot of guitar nerds think the only music worth learning is the Blues, anything else is just garbage and banging on a guitar. That should sound familiar to anyone who has done anything with horses. I think it is more about how some people act about hobbies they spend a lot of money and time on and are passionate about.
Here is the thing though. In this industry you have to keep in mind that if you stay in horses long enough, and do much with them you'll see those people again and again. I have a trainer in my past I don't think much of. I don't say a word about them to anyone because they are basically fine, and I gain nothing by talking smack. The best thing for me to do is be a little better every time I run into them and let my riding and my horsemanship do the talking for me.
There are also some really great, knowledgable and humble people in horses. Those folks usually have something to say that is actually worth listening to.