Matthew 19:9
NIV: And I say to you, whoever divorces his wife, except for immorality, and marries another woman commits adultery.So, Jesus Himself said that there was an exception for divorce if a man's wife commits adultery. Mine first wife did. Am I the sinner who has corrupted the faith and brought about gay marriage?
NLT: And I tell you this, whoever divorces his wife and marries someone else commits adultery--unless his wife has been unfaithful.
KJV: And I say unto you, Whosoever shall put away his wife, except it be for fornication, and shall marry another, committeth adultery: and whoso marrieth her which is put away doth commit adultery.
As far as people being the indirect cause of the sins of humanity, well that includes everyone. What we do, for good or bad affects everyone like ripples in a pond, because humanity is a family- God's children. Jesus died for all of us, and we have the choice to avail ourselves of His Salvation.
I don't know what any one else teaches... But that's a Catholic perspective. God bless you!