Why are Catholics more liberal on sam-sex marriage?

[TDAS04]

It is a good question, considering that the Roman Catholic Church itself is not exactly supportive.  I think there are at least a few reasons why Catholics think for themselves on this issue more than Protestants, though.

1)  The Catholic Church does place a greater emphasis on social justice/human rights than conservative Protestant denominations.  Many Catholics may just find condemnations of homosexuality
inconsistent with the overall message of compassion.

2) In the US, Catholics are heavily concentrated in urban areas, especially on the East Coast.  These areas received the most immigrants, and became used to diversity earlier.  Rural America is more heavily Protestant.

3) Non-religious Catholics are more likely to identify as Catholic, while secular people with Protestant heritage are more likely to label themselves as unaffiliated.  This may skew the results.

This may not be the entire answer, but I think these reasons are part of the answer.