Arguably, We could call for suicide to be legal. After all, It's the strongest expression of someone's liberty: the choice to give up your own life. But the reason it isn't an accepted action is because today, We know that suicide is, In almost ALL cases, NOT an outcome of a logically thinking person. Most people who commit suicide are mentally ill; something chemically or internally is "broken" or "defective" at the point that they experience suicidal tendencies. Whether you believe in God or not (both the Bible and Biology are, Surprisingly, In agreement here); suicide is not an act of nature. It is an expression that something in a person or organism is very, Very wrong.
Biologically, Organisms exist to survive. Suicide is the very antithesis of adapting to survive; the very opposite of what nature intends. On the other side of the coin, God condemns suicide; because life is a test, And to just "give up" and condemn yourself from His Earth is a betrayal of His providing you free will. Probably for the only time in awhile, You see that evolution and God are in agreement here.
Abortion, On the other hand, Is different: religious people who abhor the idea of abortion would also equally abhor the idea of suicide; both, In their eyes, Are acts of defying God's will and mercy. Therefore, You may disagree with abortion, But chances are, You can clearly see the difference between abortion and suicide.