He decided he would show them force. And personal force he did show. But that was not what God had called for, and Moses did this in anger. Anger is a dangerous sin, to all God's people. And he tells us to avoid it, flee from it.
Anger always leads to other sins.
It is one of those root sins, which always unfortunately bears other blossoms. It is complex in nature, and inevitably flows into other sins. Scripture has its own way to deal with anger. Yet, humans have conceived of other methods. It is amazing how we can invent measures which are exactly reverse of God's ways.