Amy doesn't reason very well, just answers questions, so let me see if I can explain this a bit better.
A student can only record themselves, and not breach the rules of the school doing so. So if they want to record themselves, say, practicing in the gym, they can. The 'incidental' part means, if Clover walks by as someone is recording themselves practice, her "don't record me" rule won't overrule the other student's parameter. It's against the rules to record someone else, and no recordings of anyone undressing, getting dressed, or undressed will be recorded, period (though Amy can still alert the faculty that someone is doing somehting wrong while in such state).
As for getting past the defences without alerting anyone, Emmet's the only person with any chance whatsoever of doing that, and that chance is slim to none. He's got a much, much larger chance of getting caught. And not even Stockov could breach the defences from outside the school, and she built it.
As for why the school does it, it's part of security. A little big brother, yeah, but no one's forcing anyone to be there. There may be other reasons for it, but I won't won't get into that just yet.
This is to help you understand, Shal, but you can have Clover continue being paranoid if you like.
