The difference is that securing the border does not infringe or erode any constitutional freedoms - random searches do.
The problem with this measure is that is both futile and infringes on constitutional freedoms. The futility and ineffectiveness of the plan wouldn't be that big of a deal if were more friendly to the constitution. And for what it's worth, the constitutional issues wouldn't be as big of deal if it were a very effective approach.
This approach however does nothing but erode freedoms and inconvenience law abiding citizens.
It may well be futile but I doubt you'll find many courts agreeing that it is unconstitutional. The 4th Amendment is one of thos amendments that lends itself to "interpretation". One mans reasonable is another mans "unreasonable search".
A city that requires bags to be searched as a condition for using public transportation during times of war would almost certainly win their case in court. A city that requires every homeowner to allow police to search theri property would almost certainly lose their case in court.
Reasonable vs unreasonable is all very subjective.
then any type of law enforcement, taken as an attempt to prevent an act from occuring, rather then investigate it after it has occurred, violates the constitution.
do I have a constitutional right to fly on a plane anonymously? why are they asking for ID and examining the lists of passenger names? the searching of trucks entering NYC tunnels - that violates the 4th amendment too, so we must do away with that I guess.
what can we do domestically to provide some deterrent? between the left and the libertarians, we might as well just surrender domestically.