Fr. Thomas Williams has a fine, succinct article explaining that to welcome a person is not to welcome everything he may do, too. Here's an excerpt:
There is a difference between a church saying “We welcome all persons” and “We welcome all behavior.” After all, two things distinguish Christian belief: a body of doctrine and a moral code. Following Jesus entails both. Jesus welcomed prostitutes, but he never welcomed prostitution. He was soft on adulterers, but unyielding on adultery. After forgiving the adulterous woman, in fact, he adds: “Go and sin no more.” And the tax collector Zacchaeus, on encountering Jesus, promises to pay back all those he has cheated — fourfold. Jesus never welcomed cheating, but he did welcome reformed cheaters. This is not just a matter of semantic hair-splitting. Jesus came to call sinners but to condemn sin, much as a doctor heals sick people but eradicates sickness.
Go and read the whole thing.