One of the first hits with your google search terms is explaining the issue very objectively, with no noticeable "vitriol" or "extreme hate": Here's why you should stop blasting music on the trail (one of the most important parts is not about humans at all, but about damage to the animals).
So I won't repeat all those points. You have certainly seen them, and disregarded them, or you wouldn't be asking.
So the fundamental bastion we have to look at is ethics. Very practically, if you check the entry on "freedom" on Merriam-Webster, you get two different meanings (and a third which is not relevant here):
- A: The power to do what you want to do: the ability to move or act freely [...].
- B: The state of not having or being affected by something unpleasant, painful, or unwanted.
Coincidentally, these two conflicting meanings are exactly the two aspects that are relevant for your question. This, in a nutshell, is why you are finding that the issue is so contentious and hotly discussed.
As you can imagine, every person probably is placed on a spectrum amongst these two extremes (and for different topics, this may be a different stance). For example, 99% of people are probably preferring the freedom to be free of pain. In some countries, many enjoy the Freedom of Speech (or suffer because they can't). And so on.
Regarding the outdoors (especially in hiking), many people most certainly enjoy being free of unpleasant or unwanted things. Even if someone plays music that I in principle like, when I'm hiking, I'm generally not in the mood for that music. Unless I'm a trail runner and blasting my favourite motivational soundtrack in my earbuds, there is a likelihood that I wish to have the freedom to do what I want to do: to walk in a quiet, natural environment.
Walking quietly, I am not infringing on anyone else's freedom. Everybody else who wants to do the same, can do so: everybody else has freedom A. By virtue of me being more or less unnoticeable, everybody else has freedom B as well. If I am suffering because I cannot play my favourite music, my own freedom A is reduced. Net sum: 1+1-1 = +1 overal freedoms.
If I am playing music, then everybody else around me loses the freedom to hike while hearing what they want (A), and the freedom to not be affected by something unwanted (B). My own freedom A is fulfilled. -1-1+1 = -1 overall freedoms.
So, in a simple utilitaristic viewpoint, if everyone is not playing music, the overall freedom of the whole population of hikers is maximized. Yes, my own enjoyment may be reduced because I am restricting my own freedom A. But I still have the other freedom B, so it's a zero-sum for my freedom. But for everyone else, they get A + B, so a healthy "+2" count.
If, on the other hand, everybody would play their favourite music, I would get my freedom A, but with a very high likelihood, my freedom B would be hurt - other people would blast music which I do not care for (I have very specific taste in music and it is highly unlikely that I ever meet someone who plays "my" style)! Or the fact that we both play music at the same time might make it unenjoyable for both of us.
So by simply looking at it logically in one of the simplest possible ethical frameworks, it should be clear that this is were the value of restraining yourself lie, and why you should not play music on a trail (and overall try to be as invisible or inaudible as possible).