The first demand of socialism is tacitly based upon atheism. It demands perfect equality of rights and of the conditions of life for all, and that in every regard, but chiefly in social life.
Every inequality in social life is characterized by socialism as an unbearable fraud and oppression.
Although reason and revelation teach that the servant should be subject to his master, the inferior to his superior, the wife to her husband, and the child to the parent, and that for conscience' sake, because it is the will of God, yet socialism considers all this as a violation of the equal rights and duties of all. Link (here)
In the socialistic theory society or the state has the unlimited right of disposal over every individual; that every one is destined in the first instance for the service of the community, and that for the mere purpose of industrial production.
This is the pagan idea of the state as we find it in Plato and other heathen writers. It does not tolerate any personal rights as against the community ; it also virtually denies that the first and highest end of man upon earth is the service of God and the attainment of perfect happiness after death.
As a logical consequence of this pagan view of the state and of the individual, socialism unduly exaggerates the importance of industrial life or the production of wealth. Link (here)
The German social democracy in its official platform declares religion to be a " private matter." Thus the socialistic state, at least, is altogether divorced from religion, —non-religious and atheistic.
And since the entire education of youth, according to socialists, is the business of the state, it follows that education should take no cognizance of religion ; in other words, that it should be non-religious and godless.
The community as such should not concern itself with God and religion, but must consider both as equally indifferent. Such principles can manifestly proceed only from contempt of religion, and can only lead to open persecution of the Church. Let us suppose that the Church wishes to erect bishoprics and parishes, to appoint priests for the care of souls, to control the religious education of youth, to make laws and regulations in regard to marriage, to institute feasts, etc.—would, in that case, the socialistic state leave the Church at perfect liberty? Would it be possible for church and state, which are both concerned with the same human beings, to avoid a conflict? And if the socialistic state would force priests and religious, nay, even bishops, to abandon their vocations and to contribute their share to the public production of wealth—would not that be an open violation of the Church's rights ? Would it not lead to perpetual conflicts, which would finally develop into downright persecution ? And what would be the result if the Church would claim a right to at least so much ground as would suffice for its churches, convents, parsonages, hospitals, seminaries, etc., and, moreover, if it should demand labor-power and materials for the erection of such institutions? Would not the socialistic state, in that case, from its standpoint, be forced flatly to refuse such demands on the part of the Church, and thus violate the Church's most sacred rights, and take away, as it were, the ground from beneath her feet?
The apparent permission of religion in the socialistic state as a private affair is, therefore, a mere illusion. Socialists are riot prepared to give offence to those who still maintain in their hearts some attachment to religion by demanding from them all at once the surrender of religion.
Of its very nature socialism is the enemy of every religion which undertakes to raise the aspirations of men from earth to heaven, and to preach to man that he does not live on bread alone. Link (here)
These are just a few excerpt from the book entitled Socialism Exposed and Refuted, by Swiss Jesuit Fr. Victor Cathrein, S.J.
Link (here) to the Socialist Ten Commandments