Ten points for using the word "fungible". :-)
Glad somebody did; it's not a difficult concept at all. Say you really want to buy a $1000 TV but you can't afford it. Then someone hands you a $1000 check with the stipulation that it can only be used to pay your rent. Even if those terms can be enforced you're in great shape; you use that check to pay rent, and use your money that *would* have gone to rent to buy the TV.
Now replace "rent" with "food" and "TV" with "nuclear weapons" to see why giving "humanitarian" aid to murderous dictators is a phenomenally stupid idea.