As we dont have the gaps in my country my guess is it a US interpretation of Jeremy Bentham's panopticon as applied to the shitter.
I expect in the USA people, particularly the out groups, are believed to be inherently criminal/immoral and need to be observed to make sure they aren't doing anything undesirable.
As the US public toilet is primarily a place for moral judgement and not elimation of waste you then get the crazies questioning if people's gender and equipment meets moral standards for use of the facilities based on casual assessment of their appearance.