It's easy to think of the good stuff and there are a lot of spiritual people who believe in God, but they don't believe in Satan. They don't understand why a loving God would create such a place let alone send people there, but this is a topic for another day.
Believing there's a heaven is kind of like the proverbial carrot; it's motivating towards living a good, spiritual life. Believing there's a hell is like the proverbial stick; it does in fact lead some people to living a good life and positively impacting those around them (shining their light). It's a motivation of fear (not good), but it is motivating nevertheless.
The bottom line, because of how things are naturally structured in life, I believe there's a heaven and a hell and that both can motivate us to have a good relationship with God. As we go out and evangelize (spread the good news in whatever way we can such as demonstrating the love that Jesus talked about), let's not forget how important it is to help others personally, professionally, and more importantly, spiritually, because their existence depends on it. Thanks!