Why do people risk death by joining Starfleet if not for money or preservation of their homes?

Watching Star Trek made me think of a few "deeper" questions about Starfleet, which are all related to the Star Trek TV series.

So, let's take for example the Dominion War: people are dying every second, ships get destroyed and cadets are still joining although they know they are probably going to die unless they are with Picard or Sisko.

As I read and got to understand, money has no value anymore, latinum is the general trading currency in the universe. But people on Earth don't trade and don't earn their paychecks. Earth is a much better place than today and yet young boys and girls from every culture/civilization are joining Starfleet as they are willingly signing their death note.

Why are they joining, what motivates them? They might know that they're probably going to die.

They don’t earn paychecks. They could be doing any other job, yet they choose this. And what's more interesting how many died on battlefields must be lined up in front of StarFleet every day?

What do they receive after service? Why are they doing it other than preserving their homes?