I think passive surveillance with cameras in areas that are vulnerable to crossings but far less likely than other areas where we might want a stronger presence is extremely reasonable.

Without them you have massive blind spots which can be taken advantage of as soon as people realize that attempting illegal entry through the easier areas which are being monitored is likely to result in failure but there are locations which aren't being monitored in any way. The expected response to making it harder for people to cross illegally in one area is that they will try another place to do it.

Keeping an eye on those areas in the most cost effective way possible is the ideal. Keep in mind that the people illegally crossing today are mostly looking for higher paying work and citizenship for their children. Still they've already demonstrated that they can be very determined. The people crossing illegally tomorrow will be much more desperate and looking to survive. Intentionally leaving yourself blind to huge areas to save a few bucks on cameras is basically setting out a welcome mat.

The welcome mat is not the lack of cameras on a barren deathscape of desert.

The welcome mat is the understaffed border control ports of entry where the majority of problems arise.

Cameras in the desert address only the uninformed fantasy of how illegal immigration works.

I'd agree that the lack of adequate enforcement at ports of entry is a major part of the problem and it would be good to correct that as well.