No, definitely not. I guess it depends on how you would define humanism (and Christianity), but to me they seem mutually reinforcing, at least in theory if not necessarily in practice. There are certainly many outwardly practicing Christians who are not humanists and many humanists who are not Christians, but a Christianity based on love, compassion, decency, tolerance, and openness to other people seems to me an essentially humanist philosophy.
That is defended by the First Amendment of our Constitution
