"Entering the country illegally is illegal" is restating the law. Such a statement would likely take on more meaning given the context in which it was said.
I don't agree the implication is obvious at all. Interpreting it that way make it a total truism - nonsensical unless interpreted within a greater context.
And it looks to me that's just what the GP poster was trying to do - challenge others to argue with a truism while pretending that the context in which it was stated isn't relevant.