Will the border patrol get there in, say, 20 minutes? And we have cameras covering all the land within 20 minutes of the border, so we don't lose them in that time?
More people on the ground does cost money, but the good news is that those government jobs would be a real boon for people living near the border.
Yes, and I'm no fan of the so-called constitution free zones and the impositions on our rights that result from them. Thankfully, just as borders don't need to be 100% open or 100% closed, enforcement can also exist on a spectrum and to prevent border crossing most of the focus should be on the border itself and what's happening on the Mexican side (or indeed the Canadian one, but while there are problems with people entering illegal from our northern border it's at nowhere near the scale of the problem the southern border is because Canada is a more developed nation and a lot more careful about enforcing their own borders than Mexico is).
Again, there isn't low evidence for the effectiveness of cameras. They are a proven technology. It's primarily been the rest of the systems which failed (non-working camera purchased, bad contracts, bad contractors, lack of staff to respond etc). If you know of a better solution than cameras for monitoring large areas of the border for illegal crossings I'd love to hear your pitch
As much as people hate the idea of a wall, and the entire concept has become politicized, it would make that process a lot easier, but the truth is that if you're going to monitor a border and prevent people from illegally crossing it, that will involve humans having to drive/fly out to wherever there are people are crossing in order to turn them away or arrest/process/deport them.