What is Secular Humanism?

Secular Humanism is a particular worldview based on the principles of the Enlightenment. Typically, it dismisses religious affiliation or faith as beneath the dignity of the human person, who by reason and intellect alone, is capable of self actualization. Two of the most quoted phrases in this regard come from the 1973 Humanist Manifesto: “No deity will save us; we must save ourselves,” and “We are responsible for what we are and for what we will be,”
The principles of Secular Humanism can be found in the three “Humanist Manifestoes.” The first was published in 1933 by its principle authors, Roy Wood Sellars and Raymond Bragg, with 34 original signatories. It had fifteen principles which defined it as a “belief system” and saw itself very much as a religion which would eventually supersede other world religions based on divine revelation.
The second Manifesto, written by Paul Kurtz and Edwin H. Wilson in 1973, was intended to be an update of the previous one on its 50th anniversary. It contains the quote above. The significant development of this manifesto was its call to using the public education system as a means of spreading and inculcating humanist principles in the young people of America.
The third, and much briefer Manifesto was published by the American Humanist Association in 2003. It lists six principles of humanism:

§ Knowledge of the world is derived by observation, experimentation, and rational analysis.
§ Humans are an integral part of nature, the result of unguided evolutionary change.
§ Ethical values are derived from human need and interest as tested by experience.
§ Life’s fulfillment emerges from individual participation in the service of humane ideals.
§ Humans are social by nature and find meaning in relationships.
§ Working to benefit society maximizes individual happiness.

While these sound innocuous enough in and of themselves, in reality most humanists do not coexist well with people of faith. A quick review of the AHA website reveals a central belief that faith and reason are intrinsically opposed to one another. The rejection of any sort of divine revelation leads to actions which directly oppose religious influence wherever it is perceived to exist.
The Church, of course, sees not conflict between faith and reason. In fact, as the Holy Father has said repeatedly, the human intellect reaches its greatest heights when it is informed by faith.