There is sooooo much nonsense spouted about spanning tree because it is mis-understood. It is one of my favourite protocols.
It won't kill the network. It will shut down an interface (the interface with the highest port cost) that leads back to the root bridge from the switch with the highest priority (if set) or highest mac-address if priority is left at default, but traffic can still reach every switch, and therefore every host. As long as path cost and interface cost are left the same, the attached diagram shows how spanning doesn't break networks, it fixes them.
