You believe people would not become Starfleet officers if they had no financial need to do so?
No, not really, just that *there are still jobs* even in the perfect 24th century utopia, and Starfleet is an example of that. People still have jobs and they get paid (in Federation credits) for doing so.
I don't what this has to do with your earlier statement that Earth being a paradise is a ridiculous notion.
It's just that people keep saying that the Federation has no money and *that* is what I find ridiculous. Partly because there's evidence against it, and partly because it simply wouldn't work.
Stop transposing your mentality onto technologically advanced society that works in different ways.