The Church *does *have that responsibility. If she didn’t have it, it would be morally permissible to turn a blind eye to immoral laws and policies:
“It is the duty of citizens to work with civil authorities for building up society in a spirit of truth, justice, solidarity, and freedom” [CCC 2255]
"Citizens are obliged in conscience not to follow the directives of civil authorities when they are contrary to the demands of the moral order. “We must obey God rather than man.” [Acts 5:29] [CCC 2256]
"It is a part of the Church’s mission to pass moral judgments even in matters related to politics, whenever the fundamental rights of man or the salvation of souls requires it…" [CCC 2246]
“As far as possible citizens should take an active part in public life.”
[CCC 1915]
Pope Benedict XVI stated:
"The Church wishes to help form consciences in political life and to stimulate greater insight into the authentic requirements of justice as well as greater readiness to act accordingly, even when this might involve conflict with situations of personal interest. . . .The Church cannot and must not take upon herself the political battle to bring about the most just society possible. She cannot and must not replace the State. Yet at the same time** she cannot and must not remain on the sidelines in the fight for justice.**
vatican.va/holy_father/benedict_xvi/encyclicals/documents/hf_ben-xvi_enc_20051225_deus-caritas-est_en.html (28)
Pope John Paul II stated:
Opposition to intrinsically evil acts that undercut the dignity of the human person should also open our eyes to the good we must do, that is, to our positive duty to contribute to the common good and to act in solidarity with those in need.** The fact that only the negative commandments oblige always and under all circumstances does not mean that in the moral life prohibitions are more important than the obligation to do good indicated by the positive commandment. Both opposing evil and doing good are essential obligations.**
vatican.va/holy_father/john_paul_ii/encyclicals/documents/hf_jp-ii_enc_06081993_veritatis-splendor_en.html (52)
The following quotes are from:
usccb.org/faithfulcitizenship/FCStatement.pdf
"The Church equips its members to address political and social questions by helping them to develop a well-formed conscience. Catholics have a serious and lifelong obligation to form their consciences in accord with human reason and the teaching of the Church.
"Catholics may choose different ways to respond to compelling social problems, but we cannot differ on our moral obligation to help build a more just and peaceful world through morally acceptable means, so that the weak and vulnerable are protected and human rights
and dignity are defended.
"There are some things we must never do, as individuals or as a society, because they are always incompatible with love of God and neighbor.** Such actions are so deeply flawed that they are always opposed to the authentic good of persons…They must always be rejected and opposed and must never be supported or condoned.**
"… Racism and other unjust discrimination, the use of the death penalty, resorting to unjust war, the use of torture, war crimes, the failure to respond to those who are suffering from hunger or a lack of health care, or an unjust immigration policy are all serious moral issues that challenge our consciences and require us to act. These are not optional concerns which can be dismissed. Catholics are urged to seriously consider Church teaching on these issues. Although choices about how best to respond to these and other compelling threats to human life and dignity are matters for principled debate and decision, this does not make them optional concerns or permit Catholics to dismiss or ignore Church teaching on these important issues. Clearly not every Catholic can be actively involved on each of these concerns, but we need to support one another as our community of faith defends human life and dignity wherever it is threatened. We are not factions, but one family of faith fulfilling the mission of Jesus Christ.
I don’t know if the CCC states anything about opening “our borders to any and all who want to come across.” But the USCCB does have this to say:
"The Gospel mandate to “welcome the stranger” requires Catholics to care for and stand with immigrants, both documented and undocumented, including immigrant children.
Comprehensive reform is urgently necessary to fix a broken immigration system and should include a temporary work program with worker protections and a path to permanent residency; family reunification policies; a broad and fair legalization program; access to legal protections, including due process and essential public programs; refuge for those fleeing persecution and exploitation; and policies to address the root causes of migration. The right and responsibility of nations to control their borders and to maintain the rule of law should be recognized.
usccb.org/faithfulcitizenship/FCStatement.pdf (83)