As an occasional contributor to both Answerbank, and to this forum (though not recently,) my thoughts for what they are worth are these. People enter competition puzzles presumably hoping to win a prize, and/or to see their name in print. If people are able to enter these puzzles because they have got answers from someone else, then that diminishes the chances of you winning what is effectively a raffle, so it is perfectly reasonable to feel that these forums should not exist. This of course applies to the Listener and every other competition puzzle.
On the other hand, I want to see the Listener crossword continue to appear every week, so if people can be encouraged to try it, and the weekly entry numbers do not drop, then that is 'a good thing'. As newcomers gain expertise then hopefully they become less reliant on forums. In the past I have argued here that people can be too quick to seek help on this forum, and perhaps undervalue the satisfaction to be gained from puzzling out something eventually, unaided. (I know not everyone may have the time available that I have.)
Answerbank is a forum where people discuss tv programs, news stories, tell jokes etc etc so again it is perfectly reasonable for those who contribute to the Listener threads to consider it as a place where they discuss the latest puzzle, trying not to give anything away. Some contributors want to be first to post, or come across as smug, but you could say that about Crossword Solver threads as well!