If you shoot that shot, you give up ball in hand behind the line to your opponent. Usually for unsportsmanlike conduct to apply, the player is taking some kind of unfair advantage outside the normal way the game is played. The only advantage he gains, since he is giving up ball in hand behind the line in the kitchen, is that he is not shooting the slightly more difficult shot to accomplish the same result: shoot the cue ball into a side or foot pocket.
The main point of adding the "cue ball remains in hand for the incoming player" rule was to prevent the jaw freeze as a useful strategy.
It is almost time to begin revision of the WPA rules for January 2013. Perhaps this is one of the things that needs to be clarified, perhaps in the Regulations.
