The only criticism I've heard of this fence is that it's not going to stop all illegal border crossings. Well of course it won't, but it will stop a big percentage of them.
I've never understood the arguments against this fence. It's as logical as locking your doors at night to keep out burglars. Of course, locking your doors is not going to stop every attempted burglary, but how dumb would it be to sleep with all the doors to your house wide open every night? That's exactly what we're doing as a nation without that border fence.