This as opposed to your scenario where everyone is taken care of by everyone else, regardless of their merit.

It may appear that way on paper, but i doubt it will play out that way.
People become 'worthless' because nobody wants to pay for their work.
There is plenty of work for them to do, but just none worth the time of the crapitalust to exploit them for.

In my scenario, these people do work that isn't getting done right now for lack of a budget.
I would presume that we would structure things so that on any given day they can walk down the block helping their neighbors with what they need help doing.

When the space ports open there will be no shortages of volunteers, I'm sure.
Somebody will have to do the work those folks were doing.

The way of communism as it's been is either successfully or unsuccessfully portrayed time and time again is anathema.

:Rollseyes:
Wasn't that list long enough for you?
Whenever communism, not marxist socialism, was tried, the crapitalusts bombed/machine gunned those folks from the air.
Until you can show me that zomia, or Rojava, has failed, this is a dead issue.
You lost.

https://nsarchive2.gwu.edu/NSAEBB/NSAEBB109/
https://en.wikipedia.org/wiki/Mexican_Air_Force#Chiapas_conflict

Just because you aren't aware of the lies fed to you as gospel, or omitted by those controlling your information sources, doesn't make them any less false.

Let merit lead the way, and let the people intelligently decide where their charity should go.

Sounds suspiciously like freedom.

If you send the message that everybody ought to get everything for free,

Very few people will 'get things for free'.
I can see why you might be confused.
Equating not trading your labor for bankster notes to buy at a discount to your wages may seem free, but the work still has to be done.
If that worker isn't getting what s/he needs to keep working, they will stop.

If what that worker needs is diamond encrusted dog collars isn't it better to not filter that through the bankster's profits first?
Bankster profits tend to drive up price while contributing nothing to the labor pile.

The system becomes so unsustainable that they need to keep finding new classes of "worthless people" because free energy does not exist in the realm of manpower.

Put 'nairu' into duckduckgo.
Crapitalism has to have worthless people to keep wages low, and slaves on the plantation.

The maths of eating the wealthy,...

We don't have to eat the rich, just stop slaving for them.
Let them get jobs, instead.
Nobody rides for free.

Did you read The Conquest of Bread?
Most of us won't need to work the 20k hours, the robots will replace us and we can pursue higher purposes, like helping our elderly neighbors mow their lawns rather than exploit their inability to do so for themselves for our own 'profits'.

it always leads to genocide,

Seriously?
From the mouth of someone professing crapitalism as panacea?

How many people did boeing and raytheon kill today, and yesterday, and the day before, and the day before that?
How much profit did boozeallen make on the backs of a million and a half dead iraqis?

Who do you figure got paid to bury all those bodies?
How much profit did the banksters make trading that labor for banknotes and again when those banknotes got traded for goods?
Open your eyes, human!

All hail, crapitalism! 0.o

and then the next hopefuls who get sold a false bill of goods will say...

Smdh, free your mind, slave.
Develop your own ideas rather than blindly accepting authority as authoritative, eh?

I know i have showed you things you didn't know existed.
There is much more that you should know before declaring your utopia superior to another.
You won't get those facts from authority, nor the corporate talking head on the flashylight box.

You will need to seek many sources of data, grok them fully, then move forward with your own ideas.

Or don't, and tyranny can do your thinking for you.