The key to Catholic social teaching is that charity is an obligation for all Catholics and that this is to be done at the most local possible level, which is why historically individuals and churches have been the champions of the poor whose focus was to help those in need get out of poverty. This is why the church has always had a strong social ministry in education because there is no surer escape from poverty than education.
The evil (and we should not mince words about this) of socialism is that under the guise of "caring" and "concern" it intentionally enslaves the poor by institutionalizing poverty and creating a culture of dependency (conveniently in exchange for votes in democratic governments). As I've mentioned in other posts, true charity is an opening of the heart from which many graces flow to both giver and recipient. Socialist "redistribution", by contrast, is a forced opening of the wallet which only results in resentment on the part of the involuntary "giver" and ingratitude on the part of the entitled recipient.
You have given me something to go on. I was aware of the situation with Humanae Vitae. And George Weigel has written on it. I’ll be sure to look into Pope Leo’s Encyclical.