I am assuming you mean evil is meant to be a sinful act and I have questioned this same thing in my own religion (Roman Catholic). As far as the bible is concerned nothing is said about masturbation, let alone it being evil or sinful. I think the issues of religion come into play with a very short verse said in the new testament. in Matthew 5:28 "But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart." and this is meant in the respect of coveting. So from here we need to establish what lust means and how it pertains to masturbation. If one masturbates using �naked people movies� material this would fall into a lustful nature. But now we need to establish what �naked people movies� is. Since there was no phonographic material around when the Bible was created we need to make some suppositions. In my mind �naked people movies� is the depiction of sexual acts of intercourse and anal sex. I also relate Lust to the act of looking upon someone without their knowledge. So, for me, seeing the naked body is in no way �naked people movies� as long as the actor or actress is presenting it as viewable. And if we see Lust as being one of the 7 deadly sins we need to understand that this is related to the redundancy of these sins, not the word itself. So lust, pride, slothfulness, etc. is more about allowing these things get out of control rather than it being a sin because you are proud or lustful. (Romans 6:19) "I'm speaking in a human way because of the weakness of your corrupt nature. Clearly, you once offered all the parts of your body as slaves to sexual perversion and disobedience. This led you to live disobedient lives. Now, in the same way, offer all the parts of your body as slaves that do what God approves of. This leads you to live holy lives." I think, in understanding these two versus above we can see that the Bible is preaching overindulgence rather than normal human desire. I believe masturbation to be a normal part of humanity. The material used to excite oneself needs to fall into the �naked people movies� definition for that to be evil or sinful. I see nudity as a perfectly normal thing to excite yourself with as long as it does not violate ones personal definition of �naked people movies�.