I understand how this can be frustrating - I have also found it frustrating at times, when someone criticizes or doesn't see something I love in the same way that I do. It is easy to take that personally, regardless of whether it is their intention or not.
As others have said, what you're talking about is an element of every community, especially online. But a couple things to consider.
One, no matter what we do, we're not going to change everyone else's behavior. Venting may be cathartic, but what you're talking about is almost certainly never going to change - at least in our lifetimes. Who knows, maybe in a 1,000 years we'll have collectively transcended such silliness, but for the foreseeable future...people are going to "opinionate," and in a way that at least seemingly conflates their own subjective tastes with objective reality.
Sure, you can try to change what others say and do, but not only does that generally not work, but it often leads to more problems. Plus, it can have a kind of "moral crusade" connotation that, one could argue, is equally problematic and all-too common ("Thou shalt think and behave as I think you should think and behave, otherwise you are a bad person!"). Meaning, the cousin of BadWrongFun is BadWrongThinking.
Where we have actual power is over our own response to things - how they affect us. No, this isn't victim blaming, nor is it excusing bad behavior; it is empowerment, at least potentially so. We have some say in how we respond to things - certainly more than in how others behave. We can't just ignore or magically change our feelings of hurt or frustration, but we can work with them so that we are less reactive, so that what other people say has less power over how we feel. Unfortunately there is a common trend these days that taking offense at any and everything is good and justified and leads to change (that is, changing the behavior of others). What is often lost is how we can change our own reactions, and thereby lessen our own suffering.
And just to be clear, I'm not saying that one shouldn't express to another how their words were hurtful or annoying, just that it should be balanced with working on oneself. Which leads me to...
Two, everything people say and do and think is ultimately about themselves - their own version of things - and not necessarily about the Thing Itself, and certainly not about how the Thing exists within
your world. We see the world not as it is, but as we are. That is, we all live in our own microcosm. Clearly we share the same world and our microcosms interact, but ultimately no one truly knows the world as it is - just as they (we) experience it.
So if I say, "gnomes suck," all I'm really saying is that I don't like gnomes - they suck within my own microcosm,
but not in yours (Btw, I like gnomes

)
. It is erroneous for me to think otherwise, just as it is erroneous for you to think that them sucking in my tiny universe has any bearing on their status in yours. Nothing objectively sucks, as "suckitude" is a subjective value judgement. But it is also erroneous for you to argue with me that gnomes
don't suck in my own world.
This also doesn't mean that value judgements are worthless. In any context, there are degrees of quality. I'm into fountain pens, and I can say with a good degree of confidence that certain pens "suck" more than others. But I don't really think of it that way; rather, I turn it around and say that A) there are degrees of quality in terms of craftsmanship, and B) I have personal preferences that adjust A accordingly.
The cheapest, throw-away fountain pen doesn't "suck," but it also doesn't mean that it is of equal quality to a $200 pen, or that everything is the same, and it is all a matter of opinion. A vintage Pelikan is a beautiful thing, and should be honored as such. It is absurd to say that preferring a vintage Pelikan over a $2 throwaway is just a subjective opinion, which essentially negates any kind of discernment or sense of quality. But if you love your $2 pen, it is also silly of me to say, "You're wrong in liking that pen because it sucks."
Or we could look at ice cream. All ice cream, even the cheapest of grocery store brands, is pretty good. I mean, I'd eat it and probably enjoy it. But that doesn't mean that premium brand ice creams like Ben & Jerry's or homemade gelato aren't "better."
But if you prefer Haagen-Dazs and I say, "Haagen-Dazs sucks," it shouldn't be taken too seriously, nor should it be taken as a threat to your enjoyment of Haagen-Daz. Clearly Haagen-Dazs doesn't "suck" - even if I prefer B&J - and to say it does is probably just hyperbole on my part. But even if I did think it actually sucks, that's OK - I'm allowed to (and maybe it does "suck" in my own world).
So I think it is worth remembering that not only is there "no accounting for taste," but people speak certain ways that aren't necessarily literal equations of how they feel. Some people are just really opinionated, or like to express themselves in an overly passionate manner; for example, "Gnomes suck" rather than "I'm not really into gnomes - they don't fit within my personal aesthetic for fantasy gaming".