If they enter it illegally, that's probably a crime (I have no idea of what it's like in the US).

Of course visa violations aren't a crime, did you ever had to fill administrative papers? What if misfiling your taxes was a crime, regardless of intent? Do you want everyone who made a mistake on their taxes to go to prison preventively? Or only fraudsters?

Overstaying a visa, which is the most common way to be "illegal" is literally not a crime and is not handled by criminal courts in the US. It is strictly a civil matter handled by civil courts (which can't impose jail time, by definition.) Sneaking into the country is a federal crime (a misdemeanor for the first offense and a felony for the second) and is handled by criminal courts.

I would rather no border control at all than a secret nazi-like police who are loyal only to their dear leader. We have law and order. There is a proper way to do things. Only fools think dismantling the system will work to their advantage.

Yes, you got it right.