There are at least three different reasons you might be seeing this.
The first, and I would expect the largest, is that criticism is not a question. If I go to Travel.se and write a long post about how bad it is to go to other countries on holiday, it will end up closed and probably deleted not because of the opinion it expressed, but because an opinion is not a question. In other words a long post about how great it is to go to other countries on holiday should meet the same fate.
Now you may be able to shoehorn a question ("what can I do to minimize these terrible outcomes?", "how can I find a provider who won't do the awful things most providers do?", "how can I get trustworthy information about the side effects of something I've been prescribed?") into what is mostly a criticism of providers, their common practices, or particular medications. You may then run into the second reason, which is that people in a site about X are usually pretty invested in "X is good" and get angry when they read long screeds about how X is awful. They may then react with downvotes. Enough of those will remove your question from the front page. They may also feel "I can't answer this person's question, because I don't accept this person's premise, and in fact none of us can answer it so it should be closed." Enough of that and you can't have an answer added. We can argue that this reaction from the experts and enthusiasts in a site is wrong, but that won't change it. You could work on how to word your question so that it very clearly is a question, and you might leave out some of the background detail if it isn't actually needed to answer the question. There is no need to prove that you have a good reason to ask something.
The third is that you are imagining this effect because you only notice the disappearance of your own content or content you agree with, and you don't notice when the wildly pro-X questions disappear, perhaps because you don't have the rep to see deleted content from other people. There may be some of that. Perhaps for every ten things you post, 7 are poorly received because they are not questions, and 3 are poorly received because the people reading them are, well, human, while meanwhile out of 10 similar posts that are pro- the things you are anti-, 7 would disappear for not being questions, 1 would fall afoul of human emotion, and 2 would stay. You would end up observing a 2-0 "win" for being pro-X but that's not the underlying reality. Seeing the 7 deleted pro-X points would make it clearer to you.
These three scenarios combined probably explain what you are seeing.