Murder and genocide are OT allowances, NOT NT. God only called for those acts in order to preserve a witness in the earth. And yes, the No True Scotsman is applicable because only way to determine whether one is a Christian is to examine their actions, not their words.
But your basic misunderstanding concerns the nature of God and what was accomplished by the sacrifice of Christ.
God is not a puppet-master, He is a Father, teaching His children His ways. He is preparing them to rule and reign with Him. Plus, do to His covenant with Man He chooses not to interfere when He is not asked to.