Are you saying that we should accept open sin in the church just because we are afraid that members will leave the church?? If someone is disfellowshipped and they leave the church it is not the fault of the church it simply means that they was never in the church in the first place.
Look at Hebrews 6:4-6
After you were once enlightened and have tasted the heavenly gift, and were made partakers of the Holy Ghost and have seen the goodness of God and his word If after all this you shall fall away then God says it is impossible to renew you again uno repentance.
So, if one is disfellowshipped and leaves the church after all he has tasted of God then they were never enlightened in the first place they did not have a relationship with God.
The sheep will always hear God's voice and follow him