It really would not be that hard to get past a physical barrier, especially once the word gets out about how to do so. To me, it makes more sense to have the whole virtual fence, since that tells where people are crossing and enables you to capture them before they get here.
They’re gonna get past the fence either way, so it’s better to know where they are so we can pick them up.
This requires you to trust the government to have the manpower (or the will) to go get the illegals once they are seen.