The Lord gave us both rich and poor intentionally. The rich are a test for the poor and the poor are a test for the rich. The poor must not look with greed on other men's goods, wanting to obtain them in idleness. The rich must not keep their wealth, but must learn to give it to the poor.
This test is fundamental to building Zion. Zion cannot be built without men conquering these desires and gaining the edification that comes from doing so.
To build Zion, the rich must begin to enjoy the spiritual joy and edification that comes from truly giving to the poor to the point that the rich are made low and there are no poor among them.
To build Zion, the poor must not idly hope for the bread of the laborer, and must also learn to receive without greedy eyes upon other men's goods.
You experience this yourself in a tiny portion when you partake of either side of it done rightly. The rich give freely, the poor receive without idleness or greedy eyes, and both are edified and rejoice together.
The spiritual blessings from this exchange lived to its fullest are absolutely necessary for Zion to be restored to the earth. After all, the restoration of all things isn't just an arbitrary divine checklist. Rather, Zion cannot be built without ALL of the blessings. The restoration of all things is the necessary foundation on which Zion can be built. (And if you pay attention in the endowment, you will notice a point that represents a Zion society, and it requires ALL of the blessings available in any of the previous covenants)
When the government takes over the business the whole arrangement is undermined. Just try it. Give $100 to the poor to help them in their want. Then pay $100 extra taxes to redistribute to the poor. One is personal, is approved by the spirit, and brings feelings of mutual edification. The other does not.
In fact, when the government starts taking from the rich specifically to give to the poor a perverse reversal takes place (as we see all around us) and the rich hold tighter to their riches than before, looking on the poor with suspicion and fear instead of with pity. And the poor, rather than having feelings of gratitude, look ever more enviously and long ever more openly for the government to give them more of the rich's wealth.
And that is just about the best test there is.
Wealth distribution by voluntary action is edifying to both parties. They are edified and rejoice together and we have all experienced that.
Forced wealth distribution by taxation, is not edifying to either the rich giver or to the poor receiver, and actually perversely reverses the edification that would otherwise have been enjoyed to bring both parties joy.