If hypothetically Earth did have a welfare state system without money, and the rest of the Federation Member worlds didn't, this could serve to isolate Humans on their home world.
Still, emigration would offer Humans an opportunity to live somewhere that they could succeed and be compensated for their efforts, even if they arrived with nothing. Some of my ancestors traveled to Brazil as indentured servants, but it was better than what was behind them.
Might be the reason there are seemingly so many Humans in Starfleet, it's a chance to get out.
For the first time, you might have just explained why 23-24th century humans were always so eager to colonize even when it was difficult or presented a danger.
Humans have all the food and basic needs and luxuries they could require, but they have to stay on earth to enjoy them.
The Federation doesn't prepare or support them to function in another society or place that requires currency, so basically they have
to stay on earth.
Case in point; Jake Sisko wasn't able to purchase even the simplest item, because as a human he simply had no money.
Nog on the other hand, (who was the same age as Jake) could easily do it. Jake was helpless and had to rely on Nog to do anything that involved money.
And in many societies, that would include food, transportation, shelter, clothing, basic necessities.