I believe children should be supported in loving stable homes. Sexual orientation should not be a deciding factor of whether a foster child goes to a family or not. It should be the status of the invidual/s trying to adopt and whether they are fit parents.
As for Catholic or religious adoption agencies, they should be allowed to do as they wish UNLESS they are receiving monies from the state to provide for the foster children. At this point, they are using tax-payers' money to discriminate, and it isn't fair for the homosexual tax-paying citizen wishing to adopt.