While there is some merit in having a secure LAN, I see where you’re coming from.
I assume anything leaving the LAN is insecure, and why I prefer secure protocols. However, this is often impractical for many devices and projects on the LAN side.
Should probably throw away the computer and stick to subsistence farming, just to be sure. Avoid talking to other people as well, as they may not have your best interests at heart.
I mean wifi really doesn't have a good track record for security. It's best defense is probably the short range, making searching for weak targets somewhat difficult. And I'm not even going to talk about spoofing, deauth attacks, etc. Only the newest versions have actually secure crypto, but lots of routers don't even support them (for some reason these secure features are branded as "enterprise"). This is very different from the type of security we've come to expect from high level protocols like SSL, SSH, etc.
We too were once apathetic about locking down networks. But no longer