If you buy devices from trustworthy brands and replace them when they stop getting security updates, it should be fine, right? After all, aren't 99% of home networks 'unsafe' according to your definition?
Prevailance of home ip addresses in DDoS attacks and in proxy pools does suggest so ¯\_(ツ)_/¯
Vetting devices you introduce to network is of course solid advice, but a little bit of paranoia never hurts in tech.
My whole point above that it does actively hurt, with devices randomly misbehaving at exactly wrong times. It's not enough to set up everything once because devices get updated and change ports, domains, and protocols. It also makes everything more brittle, requiring multiple inter-VLAN proxies to be running at all times for seemingly unrelated devices to work. That SD card in your raspi died? You decided to update Docker on it and run into problems? No Sonos for anyone in the house until it's fixed.
There's a real cost to that paranoia, it's just another case of security/convenience tradeoff.