There are countless threads and posts over things in this world that cannot be changed. My question is why? Why argue over things that cannot be changed-that you have no control over? It is pointless and causes too much stress! Even if you prove a point to be “right” will it matter? This may come over as apathetic, however if there is nothing that you can do in the first place, why waste time on it? There are many more constructive things to do besides this, and many more intelligent discussions to be had.
every major change is preceeded by people ignoring pleas of “the world cannot be changed”.
In any case, discussion is cathartic.
You cannot change the fact that people write about things that cannot be changed!!! 
It would help if you cited an example or two, but from what I’ve seen the majority of topics, here and on other boards, deal with the perceptions and attitudes people have toward given topics. Threads thereby serve as discussions that may indeed change these perceptions and attitudes. You seem to imply your use of the word ‘world’ entails global revolution or global political and ideological change. I would argue changing one’s perception is ‘changing the world’. ‘The world’, of course, is just a synonym for ‘you’.
Even though you may not be able to singally change a major world wide problem, it’s nice to be able to voice your opinion. It is also a calming feeling to express your ideas and share with others, building and growing as you learn. This is just my opinion, but I ask you, why are you here if it seems pointless to discuss major issues in the world today. I’m here to voice my opinions about things that really make me think, such as religion, cutting edge science, emotions, or any other topics that catch my eye. That is my main reason for writing here.
If something truly could not conceivably be changed, were absolute and constant and inviolable, it would seem rather pointless to think or talk about it; that would take time away from thinking and talking about problems that do have solutions that haven’t been figured out yet.
But until we actually have a solution for a given problem, it’s often the case that we are uncertain between two conclusions for that problem–
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We either think that no solution could or will ever exist, and maybe the way the problem is formulated is nonsensical, or…
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That there is a knowable solution, just that it is currently unknown, and perhaps the method of determining a solution is also unknown
Deciding between these two is a rather hairy maneuvre. Examples of this situation are the possibilities of artifical intelligence–compare to last century arguments over the impossibility of human flight due to a ‘natural inability’–or the idea that change in a given area is impossible.
It seems that you have a pragmatic view on things. I would say that a knowledge of things “that cannot be changed” is just as valuable as things that can be changed. Are natural laws useless things, or is cosmology useless? No, it satisfies a need to understand the world that we live in.
However, I don’t see many people falling over themselves to discuss social philosophy these days.