"How many of these terrorist attacks have been perpetrated by illegals from south of the border... " The fact is that there are a lot of middle easterners sneaking into the country through the southern border because its such an easy way in.
Should we stand at the border and say..... OK Mexican illegals are "legal", but others are "illegal"...... I don't know about you, but in my book ILLEGAL means ILLEGAL no matter who is doing it!
We've had illegals coming across the border FOREVER. There is no reasonable, doable plan to 'close the border' that I have ever heard of, that would also be effective. If you are proposing putting up a barrier or posting a soldier every 5 yards, you could probably have an impact. But what would the cost of that be, and where would all these soldiers come from?
We cannot interdict every single person of foriegn origin without becoming a police state.