@Stephenson:
A take back itself is in my opinion neither unsporting nor unethical. Its the behaviour of the people who use the possibility of take-baks.
If you ask for a take-back you give me the clear signal that you want to turn the game into a friendly game/training game. There could be some reasons to accept this. But its clear that in a regular rated game thats rarely the case - I dont accept take-backs there, I only accept them when an obvious mouse-slip occured.
The problem with take-backs is that some people try to misuse them by asking for it without any obvious reason. In this case its indeed unsporting and unethical to request a take-back, especially if you are not willing to grant a respond.
Best wishes
Nada