Its better to understand how a device works then to be afraid of the unknown.
Thanks for the pointer to the S2 framework info. More security is a good thing. Just take what you read with a grain of salt. History shows that statements like this:
"S2 also completely removes the risk of devices being hacked while they are included in the network"will
be proven false over time. For now, though, z-wave is certainly the best bet for the secure smarthome.