I would say, to by default "being Illegal", yes, I consider anyone who breaks any sort of prescribed rule for a situation an "Illegal" something, (You have preformed an illegal operation, that is an illegal command, etc) by that definition, pretty much everyone is a committer of "Illegal" acts, not United States Laws always, but by some rule or another.
Aside from semantics, I would say that, while it is clear where the laws stand, it is unclear where the burden of proof stands.
For example, in a movie theater, if you suck into a movie without paying, you by default have broken a movie theater's rules, and are an "illegal viewer".
The usher’s job is to keep the rules of the movie theater, if he has reason to believe you snuck in and you cannot prove otherwise, he may throw you out.
But let's say that Viewer A purchases a ticket, it's a busy day and none of the employees can really remember her face over anyone else's, she gives the ticket to the ticket taker and gets back the stub without a word, she crumples up the stub and tosses it in a trash can. Later, at some point during the movie she leaves to get popcorn, and for whatever reason the usher mistakenly believes she snuck into the movie, what should be done at this point?
Is the usher's experience alone enough to place a customer under suspicion?
Is it the viewer’s fault for not taking care of the ticket stub?
Is it the theater's/ticket-taker's fault for not placing adequate emphasis on saving the ticket stub?
By denying the customer services, the theater would be breaking the laws of the transaction.
But if there is no reasonable measure to prove anyone "guilty", then anyone can sneak around movies without repercussions.
I would say that the logical middle ground would be to increase the means to prove the crime, secutity cameras or the like to prove the crime took place.
In the same way, I think the standard for immigration, voting, etc. should be the same, if the government wants to ask for proof for a given rule being followed, then they should ensure said proof is provided to everyone that standard applies to.