While I'm typing this post, there's a Subject: field above it. That's the Subject of my post. If anything, you should wonder why most people don't use it, and why there's a default filled in already. I know the answer: it's quite convenient to leave it as is. But if I create a new post Subject, and you quote my post, you'll get the same Subject again (unless you change it).
It's a feature, not a bug.
Okay, makes sense, but then, isn't it better for posters to essentially stick to the same subject selected by the OP instead of changing it for each post? That's basically why most people don't change it, but if someone wants, they can abuse this feature just like how the guy I mentioned did.
I understood what you suggested initially and we may disagree, that's totally fine. I simply oppose your suggestion that the Subject of a topic should remain unchangeable for anybody else except the OP. You asked for opinions, you got mine. We don't need to find consensus.
Agreed, we're just discussing, no one needs to agree with each other in everything being said or proposed, and that's totally fine.
Let me add another thought regarding consequences of your suggestion:
If the OP is the only one to define the Subject for the whole thread, I would assume that the Subject should change for every post in a topic when the OP updates the topic's Subject, no? (Of course, the Subject for any other poster could remain unchanged but does this makes sense when you allow the OP to update the Subject and nobody else can change the Subject?)
That's how I believe it should be. If a topic is created, it should be discussed with the given title, and everyone should have the same subject when they are making their posts. Only because you are responding to someone else within a thread, you don't need to specifically change the subject line for it. As long as you are and the person you are responding to are on-topic, it shouldn't be a problem, imo.
Now think about the following potential of abuse:
An OP posts a topic with some agreeable or interesting Subject. Other users chime in and post: Yay, I like your topic... totally agree... whatever...
Later the fictional malicious OP changes Subject to something really nasty and/or offensive and above assumed update mechanics is imprinted on any poster of the topic/thread. I definitely wouldn't want this.
A good poster/user wouldn't do that, and if someone does, which is usually very rare because in all the years I've spent in this forum, I've not seen that happening much, but, even if someone does abuse it, we can report the thread to the mods and they will take care of it.