It's still trust though. We trust that iFixit or some other third party would discover and publicize the secret camera. A few of us might even do it ourselves, but most of us would just trust that someone else would.
When somebody figures out how to leverage a buffer overflow exploit in order to create a camera or microphone where none exists, then the might be similar.
Software vs. hardware means you trust Microsoft to never in the future decide to spy and to never make a coding mistake that could turn the equipment on when it's not supposed to be.
When it comes to teardowns you trust that multiple independent parties aren't all actively lying to you in concert.
