To me there is no principle difference between seating scripts and "bots", since they both execute actions related to playing poker without any human involvement required. So I absolutely believe, that all poker sites should ban this kind of software.
Besides giving the user an unfair advantage scripts also tend to create excessively long waiting lists thus making it more difficult to get seated for non script users. And to add insult to injury if a seat become available, because the "fish" left, the script will discover this right away and not accept the seat.
This sometimes mean, that a table, which had 11 players waiting, might dissolve completely in a few minutes, as the regs, who were already seated, leave one by one, and none of the script users from the waiting list wants to play either, because the target is gone.