The Christian in the coliseum, about to be eaten by a lion, would not argue evil "had no effect" on him, but he would argue that evil has had no effect on his morals.
St. Paul suffered HUGE effects from the evil around him; he lost his freedom and then his life. But he did not regard being in chains and beheaded as a significant moral choice on his part.
The distinction is at the core of the entire New Testament. It is the very definition of Christian freedom.
Of course your children being around lesbians at school will affect them. But whether it affects them morally or not is a separate question, and entirely unrelated.
And the law is changing because there are lesbians. The law is not creating lesbians.
This entire subject is enough to tempt anyone to a foul mood. That the subject comes up affects me; my mood is my choice and the only part of the complex God judges me on.
The difference between the two is the line we're trying to draw. I value our exchange and offer my warmest respect, whether we agree or not in the end.
First, society and our morality are joined. Re-read Judges. Or review why Israel lost the first battle for Ai.
Second, I never said "moral impact," I said "impact".
As Christians we are called to impact the world for good. We are called to advance the Kingdom of Heaven and beat back the Kingdom of Hell until we are at its very gates - and those will not be able to stand against us.
We fight a battle on two fronts. We feed the hungry while we also attempt to teach them the Good News. But we don't preach the Gospel to the starving.
Shalom.