This gets down to the basic mindset (whether they realize it or not) of socialists/communists: ‘If only everyone would work hard and let us take what we need from them to run our programs and redistribute, everyone’s life would be better’. In other words, they advocate slavery. They're just too blinded by ideology (and the idea of being really important leaders and saving ‘the people’) that they can't even see this reality. Even if they did, their delusional grandiosity would allow them to rationalize that it was all OK, because they would be fair and good slave masters.
There is no social justice or any other idealistic wonder in socialism / communism. None. Charity is virtuous and humane, and we should all be charitable human beings. Involuntary confiscation for politically motivated redistribution is not charity - even though some in government would like to rationalize it this way.
I'll take it a step further.
Excessive confiscatory taxes are a sin against charity because they remove the voluntary link in giving that makes the giving a free will act.
Furthermore, it removes the opportunity for the recipient to be thankful and express gratitude by destroying the relationship between giver and receiver.
True charitable giving glorifies God for both giver and receiver. Government redistribution does not.