Even if manufacturers behave nicely, there is still the possibility that the devices are eventually somehow compromised by bad actors and used nefariously.

For example, the CIA developed and deployed a program to use the built-in microphone on Samsung "smart" TVs to spy on targets, even when it looks like it's off: https://www.theverge.com/2017/3/7/14841556/wikileaks-cia-hac...