Oh but it is correct. You can force a zip apart. Comparing zips to doors is like comparing apples and oranges.
Source: Old man has worked in airfreight / airline industry for decades. He has demonstrated this 'trick'. He will also never buy luggage with a zip on it.
Security staff have been subtley opening luggage for decades. The TSA locks only legitimise it...I suspect it represents some level of legal consent.
My preferred method of checking in baggage is covered in shrinkwrap and tape. Most airports ive passed through offer this as a service...not sure about Merkin airports though.