Why would Philadelphia harm children by excluding Catholic foster-care services?

The story is here:  "At the end of June, the City of Philadelphia will be terminating its contract with Catholic Social Services because of its beliefs about same-sex marriage. They will be doing this despite the fact that no same-sex couple has filed a complaint against them. They will be doing this despite that fact that the City of Philadelphia has 5,000 children in foster care and has recently asked for more people to step up to the plate to be foster parents."

Thankfully, the happy warriors at the Becket Fund are on the case.