The activities of which you speak in the OT were for a specific time, in a specific place, and for a specific purpose. Such actions were ordered by God as both just punishment for the wicked and to protect His people in order to bring about the salvation of all.

Also, keep in mind that God is not bound to do good because God has to do good things, rather good is bound to be what God does because God is the source of good. We define good by what God does (1 John 1:5, 1 John 4:8, James 1:17). True justice cannot be condemned.

There are no claims and never have been that anyone has the authority or right to such actions today. Furthermore, God will not order such actions ever again as we are in the final days awaiting His return.