[CharlesWayneCT]

I am certain that he didn't fill in the form because he was afraid they would find out he was illegal (which I'm also sure they would have, nobody leaves with that much cash without being detained).

I think he didn't understand the consequences of that act.

It's not punishment, of course. Because if it is, it's unfairly administered, since the "punishment" for the same crime is based on how much money you have.

It's not even being treated as a crime, more like a "you didn't write down any money, so you must not have had any, so we'll take it all from you, good day."

[Just sayin]

I think he didn't understand the consequences of that act.

What you aren't seeing is that your own position of excusing their action of being here illegally and working here illegally contributes to that very 'lack of understanding'. You are part of the very problem you just stated. Classic.