What do you guys think of the idea of smart homes? I could make a basic setup using https://home-assistant.io to control my home temperature and lighting; the tools for doing this are everywhere nowadays and implementation doesn't seem too horrific anymore.
But setting aside what I "can" do, is this something that I "should" do? How can a person implement this without connecting any devices to the internet?
This depends. You can be smart about it. Running your own servers, including your own NVRs for video storage. Have dedicated VLANs. Firewalls. Etc. it’s not that bad.
Granted I work in automation and robotics and now networking so I’d say I’m for sure a giant add nerd. For a normal user it can be hard to stay safe.
It's a lot easier and cheaper than you might imagine. A used Dell 7040 for $120, a ZigBee controller for $30, install Home Assistant OS on the Dell, plug in the controller, and you've got a really powerful smart home hub that can control any ZigBee device you have locally without ever needing any "cloud" services.
Since you don't need cloud services, you don't need to worry about firewalls or networking or VLANS, because the controller replaces the "required" hubs that manufacturers say you need, that force you to use their servers.
With the controller, Home Assistant becomes your hub, and the ghost of Orwell will smile and nod at you approvingly, maybe even give you a cheeky thumbs up.