The Principle of Solidarity

The term “solidarity”, widely used by the Magisterium, expresses in summary fashion the need to recognize in the composite ties that unite men and social groups among themselves, the space given to human freedom for common growth in which all share and in which they participate.
-Compendium of the Social Doctrine of the Church.

By virtue of their participation in the society that surrounds them individuals are debtors. They owe a debt to the others in society who through their efforts

make human existence liveable, and because of the indivisible and indispensable legacy constituted by culture, scientific and technical knowledge, material and immaterial goods and by all that the human condition has produced.

Promotion of division of the classes, division into employer and employee, haves and have-nots, along racial or ethnic or other lines is a violation of the Principle of Solidarity. Likewise it falls not just to the rich to promote justice, engender charity or bankroll government programs.
Class warfare, the principle upon which the idea of redistribution of wealth is based, as well as most modern interpretations of employer/union relations is based upon an adversarial relationship which violates the idea that we all have a responsibility to contribute to society.
The employer and the employee together work to make the business enterprise successful. Both benefit as does society. When demands of the employee become an unreasonable burden on the business, such that it becomes unprofitable, the employee is not a contributor to society, but a burden. Likewise for the employer maximization of profits, to the exclusion of the common good is un-Christian.
This does not mean that profit in and of itself is an evil.

Profit is useful if it serves as a means towards an end that provides a sense both of how to produce it and how to make good use of it. Once profit becomes the exclusive goal, if it is produced by improper means and without the common good as its ultimate end, it risks destroying wealth and creating poverty.
-Caritas in Veritate, BXVII

Solidarity makes it the responsibility of those who are well fed to feed the hungry, of those who have a riches of blessings to help those who do not. In this context it should be remembered that wealth is relative. Generally speaking the $22,500 which is the designated poverty level for a family of four in the United States is more income than the balance of the human population on Earth sees in their entire lifetimes. Most of our poor enjoy luxuries which are unthinkable to people in most of the world.
In this context the inequalities which exist between most Americans pale in comparison to the inequalities which exist between even our poorest and most of the world.
This leads the conclusion that every member of American society should be willing to contribute to the well fare of those less fortunate than ourselves and to the common good.
So what is the common good?
The Church speaks about that throughout the Compendium and indeed through many other documents throughout the ages. It is also very specific about what does not contribute to the common good.

No legislation, no system of rules or negotiation will ever succeed in persuading men and peoples to live in unity, brotherhood and peace; no line of reasoning will ever be able to surpass the appeal of love. Only love, in its quality as “form of the virtues”[456], can animate and shape social interaction, moving it towards peace in the context of a world that is ever more complex.
-Compendium of the Social Doctrine of the Church.

Charity is not something which can be imposed by government. Attempts to do so are disruptive to Solidarity.

Support for fringe activities, such as homosexuality, homosexual "marriage", pornography, contraception, abortion, in short activities which undermine the family are not just detrimental to the individuals involved, but also to society as a whole. To the common good.
Governments, and the individuals in those government which support such activities fracture the Solidarity of the society and work against the Common Good as understood by the Church. Such a government or administration is not acting in conformance to Catholic Social Teaching.