Agree with this, especially with the "it takes quite a bit of care even for simple stuff", but this should not discourage developers to do so.
One of the reasons to build this kind of infrastructure is to set proper standards for smart contracts development which are currently missing.
As long as we are aware that we need to be careful, and we raise the quality of the code and keep on developing tools to improve development as a whole things should keep on moving forward.
It's an operating system insofar as it's a layer of services on top of the "bare metal" that is the EVM. Through those services it allows the development of complex applications in the same way a normal OS does.
Tezos and zeppelinOS are very different things. zeppelinOS is building an operating system on top of the Ethereum Virtual Machine to provide secure infrastructure for the development of smart contract applications. A technology that is still being developed but used by thousands of developers, and maturing into it's next phase.
Tezos is building a new blockchain with a different infrastructure altogether.
Exactly. If a higher level of security and robustness of the platform is not achieved we will continue to see hacks like the Parity one over and over again.
This is one of the main drivers for building zeppelinOS.