I'm involved in scientific research and methodology, so when I see these posts about health and diet, I often fact-check them. Many are somewhere between "a little bit of truth" and "total bollocks". As a rule of thumb, the more a post or meme tugs on your heartstrings or tries to shock you, the less accurate it's going to be. Unfortunately some activists believe that "the end justifies the means" and that it is acceptable to mislead people, or not to care about truth, just so long as it persuades you to do what they think is right. In fact, the effects of dairy intake on health have been, and are being, studied on a large scale and there aren't any conclusive answers. At present the weight of the evidence seems to be that dairy intake is associated with longer life and better health, but not in all cases, and fermented foods like yoghurt appear to be more helpful whilst in some cases plain milk may be harmful. But in others it's helpful. Got that?! Science works by asking questions and trying to find more answers that add to the body of information we have, so it's an ongoing process. What scientists do is look at each study, say "OK, what could have been done better here? How much confidence do we have in the results? Does this change the weight of the evidence? How does it fit in with all the other research done?" But what some activists do is look at the results and say "Does this fit in with what I already believe? Yes? Then look no further! Share away!" . It's cherry-picking, and when someone does it, it's a big red flag that you can't trust them as a source on science.
Re your news feed, I generally do what @RainbowFairy suggests, which is block the source of the bullshit, but unfollowing your friend is a reasonable response to this too. I think that @SwarmOfCats and @MollyWobbles are right - this sort of thing is counter-productive as they end up alienating people and just posting in an echo chamber. We all differ in how much we're affected by visual images and some suffer real distress being exposed to these images. You don''t have to put up with that if you don't want to. And it's not a case of you turning a blind eye either, in case that's what's worrying you. The fact that a horrible thing happens in the world does not mean that the person posting the image has the answer to how to make the world a better place. Not infrequently, it turns out that the animal cruelty posts are as misleading as the 'darry ruins your health' ones. Sometimes (the infamous raccoon dog being skinned alive video) it turns out that the perpetrator of the cruelty was paid to do something they wouldn't normally do, in order to get a good video. Rare occurrences are portrayed as routine. The people who create this content manipulate your emotions by not providing full information.
How would you feel about having videos/adverts from proselytising religions in your news feed? From every activist organisation, ever, including those on opposing sides? If you don't think you should have to see their material then you don't have to see the animal rights activist material, either. Presumably you would unfollow a friend who just posted endless party-political broadcasts or adverts for a product they sold too. You are not obliged to be anyone's audience.
Re the suggestion that being a vegetarian is pointless compared to being vegan, it depends what your motivation is. If you want to reduce carbon emissions, veganism, vegetarianism or reducing meat intake is a positive step. If you are concerned about animal welfare, look to vegetarianism or meat eating where animals have a decent life. There are many situations where doing what you can is better than doing nothing.
If you want no animal death to be in your name or for your benefit, then veganism makes sense. If you are a believer in animal rights, rather than animal welfare, it makes sense. I don't share those views, because I'm interested in animal welfare rather than believing that animals have rights. I've known many farm animals which have had good lives. It is a big step from saying that many farm animals have imperfect lives, to saying therefore they would be better off never having been born. Does dying young mean you're better off never having been born? That's a huge value judgement and I'm glad that nobody decided I shouldn't get to live because I might suffer .