I don't think

I think "I don't think" proposes to meld two nearly similar senses. The first sense, the one it actually says, is often overlooked. "I don't think A" tells me "there are people who think A, and I am not one of them". The other sense is "I think something something negated something something". The second sense is more or less "something is not happening, doesn't exist, doesn't occur, shouldn't be done, etc." It has the unfortunate construction of NOT in the sense that it refers to a thing not existing, and leaves the listener wonder what does exist, of all possible existences. And moving the "not" to the earlier clause increases the confusion. In the second sense, there is a comforting compactness expressed by moving a negative from somewhere in the second phrase to the "I think" phrase, so that the speaker always lazily knows where to put the negative, going from "I do think A should NOT be done" to "I do NOT think A should be done". To the listener, the "I don't think" construction can be interpreted several different ways: "I think NOT A should be done", "I think A should NOT be done", and the sense of "I am not one of them".

Let's ignore the confusion and assume that the speaker means the first sense. Like pretty much everything in my discussions here, "I don't think" perniciously invades my mind without letting me consider what it means, so I'm going to return to the first sense: "there are people who think A, and I am not one of them." Notice this: even if it only means the first sense, it sounds like the speaker is stating a stand, while it in fact removes the speaker from a stated stand.

What easy thing can the speaker do to remove the NOT and clarify their statement? I think they probably have to wait a moment before speaking, and first figure out where the "NOT" really goes in the farther reaches of the statement, then they have to wait another moment to figure out what the positive statement of the complement of the negative statement is. They may have to wait. If they do, then they will take time to make sense. By blurting out the "I don't think blah blah" they waste everyone's time, theirs included.