Death is a complete unknown. Rather than face the pain he knows, clinging to another few years, days, hours with loved ones, he instead walked headfirst into what could very well be worse pain and debilitation (think any religion's hell), yet clearly in a desire to avoid the pain and debilitation that he knew.
Back in the day when the bible was written if you got a terminal disease, you would die quickly. Today we have hospitals and medical treatments that drag on the process. The people who wrote the bible back then probably lived in a world where suicide was mostly done by people running away from things not related to health, therefore they despised those people who committed suicide. People back then simply didn't commit suicide because of health problems because they would die shortly anyways if they got a disease. I think if they saw how people with terminal diseases have their lives dragged on by medical treatments wouldn't have wrote that you go to hell for suicide.
I tell them to turn to the study of mathematics, for it is only there that they might escape the lusts of the flesh. -- Thomas Mann, "The Magic Mountain"