Maybe for some, but I don't think it's necessarily true for the majority.
I have a friend who works for a government agency. Several years ago, he was loaned to border patrol or whatever it's called. During that time, I got the sense from him that the border patrol is really being asked to do an impossible task -- with limited resources, they are supposed to stop tens of thousands of highly motivated people from moving across an invisible line that's hundreds of miles long and mostly in a desert.
Then at the end of the day, they're judged on how many pails of seawater they managed to take out of the tide. They are very definitely not getting judged on whether they take a step or two over the 'constitutionally questionable' line, especially not in southwestern states. So there's no reason not to put up a camera or two.