You are right on that, but a distinction should be made as to what the Church considers “marriage” and what the State considers “marriage”, just so others don’t confuse this.
Silly logic to make this easy: When the Church says
apple, it means “
round red fruit”. When the State says apple, it means simply “fruit”.
The Church considers marriage by other religions as valid, as it fulfills the precept of marriage:
The State definition of marriage, however, does not fall under this definition. So, while non-Catholic marriage is not sinful, SS marriage (or, more precisely, what happen within it) still is.
For the Church, marriage is not simply
“fruit” = union of two persons. It is
“round red fruit” = union of a man and woman ordered towards a certain goal.
In a nutshell: the State recognizing SS marriage does not mean the Church considers those unions as valid sacramental marriages.
I blame society for all this confusion