When a person hires a personal assistant, the person doesn't generally turn around and accuse the assistant of spying on them because the assistant listens too attentively.

Sure, but the assistant also doesn't typically record all conversations and give them to the service they work for, and they also don't typically bug the entire house so they can hear every conversation throughout the house.

There's no way I'm getting a digital personal assistant like Google Home or Amazon Alexa. It's a novelty that trades privacy for a little convenience, and I'm not that lazy.

That's a personal choice you are welcome to make. I have a Google Home Mini sitting on the shelf behind my head right now, and it really doesn't bother me.

(... in fact, I tend to think about it in just the opposite way: if I'm ever murdered in my home, I want the cops to be able to subpoena Google to get evidence on who the killer was. It's nice to have a system watching my back all the time).

The Nest is not a personal assistant like the Google Home. It's a thermostat.

The microphone is not part of the Nest thermostat, it's only part of the Nest Secure, the keypad which is included as part of the Nest Guard.

Nest makes many products. This one is a security/alarm system.