They conveniently forget that Jesus's forgiveness comes AFTER the sinner has repented.
Fr. Robert Barron, who made the excellent "Catholicism" series, had a good column responding to Sullivan's article in his Word on Fire blog. Here is the link to the Real Clear Religion page with the article.
As Father Barron makes clear, Andrew Sullivan is run of the mill, with nothing new and nothing worth reading in his attack on Jesus and thus, Christians.