Can you, in all honesty, mas,turbate without sinning against the clear commands of Christ? If yes, then we are never told that the act itself is impure or forbidden. But let us be honest and admit that it is not so easy to do if we are committed to avoid mental segxwal sin.
Luke 14:28 (NIV) "Suppose one of you wants to build a tower. Will he not first sit down and estimate the cost to see if he has enough money to complete it? For if he lays the foundation and is not able to finish it, everyone who sees it will ridicule him, saying, 'This fellow began to build and was not able to finish.'"
Mastur,bation can help us find segxwal release when we cannot control our desire nor satisfy it through a marital relationship and in this sense it can be helpful. However it is almost inevitably associated with segxwal fantasies and this is where it can go wrong and lead to sin.