Recently there have been a spate of threads being created around the same time around the same discussion topic - for example these:
In this case, one thread was created from a news article posted on the front page and the other by a user directly posting a link to the article on the original article in question. This clogs up the forums and disjoints actual discussion.
This duplication of threads can also occur when there is a long-running, existing thread on a topic (such as Inland Rail) and people creating new threads as further news articles on the topic occur do not bother to search for existing topics. In this case, the merger of the 'news article discussion' thread with the existing topic would provide extra context to those unfamiliar with the topic at hand.
There are several possible ways to remedy this issue:
To merge a thread by post date is trivial, but will result in a very disjointed discussion - we will not compose merged threads so that they make sense. For this reason alone we've never built such a feature, despite how many times it's come up.Should not need to do that - as stated in the idea there are other ways this could be achieved.