There is only one sin that can not be forgiven.
Suicide. All other sins can be forgiven.
Your position has no Biblical authority.
Some Christians would define suicide as a type of murder, but I disagree. I would define murder as: The unlawful killing of one human by another. This is certainly the way the law defines it. I don't believe that we should have one dictionary for use when we speak to each other, and another dictionary when we attempt to interpret the Bible.
But, hey, I agree that suicide should be a crime punishable by death!!
Even though suicide is clearly not murder (a crime which is prohibited by the Bible); some Christians resort to the writings of Paul to show that the body is the temple of the holy spirit and therefore killing one's own body is a sin. These Christians rely on the following scripture:
Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you?
If any man defile the temple of God, him shall God destroy; for the temple of God is holy, which temple ye are (1 Corinthians 3:16-17, KJV).
Flee fornication. Every sin that a man doeth is without the body; but he that committeth fornication sinneth against his own body. What? know ye not that your body is the temple of the Holy Ghost which is in you, which ye have of God, and ye are not your own? For ye are bought with a price: therefore glorify God in your body, and in your spirit, which are God's (1 Corinthians 6:18-20, KJV).
These verses do not address suicide directly, so I suppose everyone is is free to interpret them in any way they desire. I do find it interesting that the only sin against the body that Paul mentions is fornication, which would strongly suggest that suicide was not such a sin. Besides, if suicide - which I would define as the act of hastening one's own inevitable death - is a sin, then it must also be true that any act which causes one's premature demise is equally sinful. Thus, those who smoke, drink excessively or fail to diet and exercise properly are condemned to the eternal fires of Hell.
And, finally, those who equate suicide with murder are a bunch of ignorant, insensitive morons. And I say that without malice, but with heartfelt sincerity. I truly feel sorry for you if you cannot comprehend the difference between the mindsets of those who kill others and those who take their own lives in quiet desperation. If there is a judging God, He will not condemn those who took their own lives; instead, he will heal their pain so that they can live and love and laugh again; or, as the Bible puts it, He will Restore unto me the joy of thy salvation; and uphold me with thy free spirit (Psalm 51:12).
What kind of sadistic God would torment for all eternity those who faced so much torment in their lives that they could no longer bear it?
How could anyone worship such a monster?
For the record, my 24-year old son committed suicide on January 11 of 2008.