I have read all this thread before responding .
Whether one reads all the thread, rather depends on how long it is. When it gets up to 16 pages or more it is a bit much to expect someone to read all those pages before possibly making a one sentence response that may be very significant.
Also, like ordinary conversations, threads do evolve and develop as they go and there is no rule to say every response has to stay rigidly in line with the OP, sometimes the most interesting discusssions occur when the thread has evolved into something other than the OP.
I do not think it is possible to have a hard and fast rule. Sometimes I make one response to a thread and that is it. Other times I make a response and no more for several more days when I then notice that the thread has evolved and I then comeback to it and post several responses over a day, then drop out again. I will have not read every post on the 10 pages that intervene between my first and later posts
Of course there is repetition and fatuous remarks, threads are just conversations in print and is remarkable how much repetition, irrelevance and inanity there is in everyday and, even, serious conversations!