I think this is fine. With regard to Philip's comment about the phrase from the Bible, I am a minister trained in theology and when I first read the sentence it sounded fine to me.

I think you are mixing 2 idioms. 1) People in glass houses shouldn't throw stones. 2) a phrase from the Bible: “Let him who is without sin among you be the first to throw a stone at her.” This can be simplified: 1) Do not criticise your friend if you do it also (i.e do not throw stones, especially if you have glass windows - you'll get hurt also. 2) Casting the first stone - no one is blameless/innocent. We all make mistakes or deliberate wrongs. So throw the first stone (at someone you blame) only if you are innocent. Which we are not.

David, I really don't know how much we can quote from the Bible and what is too much and contravenes Italki's guidelines. So I tried to tread a careful middle line.