I don’t think it’s so much that god-fearing people are necessarily afraid of death. I think that more often the fear of death is primary, and frequently people manage this fear by finding something greater than themselves to identify with.
I share your concerns as well. When I was young I couldn’t understand why people who believed in heaven and hell wore seatbelts. If worldly existence is a vale of tears, then why not hasten one’s passage to their eternal rewards?
When I was even younger, I felt like my nihilism also justified suicide. In a state of depression, nonexistence beats the hell out of struggling to survive in a world that is harshly painful and ultimately pointless!
My current position is that I just don’t know what happens to the thing I call “me” upon the expiration of this human body. I don’t even know precisely what this “me” even is. Isn’t it necessary to be clear about what I
am today before I start investigating whether there is an “afterlife” or not? I currently suspect that the question is less important than what can I do today that would reduce the suffering of all people, including myself.
Regarding the taboos over discussing suicide, I believe that culturally the larger topic of mortality is too unsettling for most people to contemplate. In society, we hide away from any awareness that death is even a thing. People who are near death are not included in daily life. Our cultural and entertainment tendencies are arguably an elaborate system of distractions from the fact that we all will die. For more on this idea, you might want to look into terror management theory at this link:
https://en.wikipedia.org/wiki/Terror_management_theory