I kinda don't care what other countries treat as a crime. (Some consider things like criticizing the government and being homosexual to be crimes, too.)
Regarding the US law, it is a misdemeanor to enter without the approval of a border agent. A fine and no more than 6 mos in jail. In state court, that kind of thing is often eligible for a deferral/diversion program or expungement.
The "real" problem (IMHO) are the people who actually enter legally, and either intentionally or unintentionally, overstay their visa. They successfully avoided that misdemeanor crime you mention, so are not "illegal." They have remained "unlawfully" but have not - from what I can tell - committed a crime.
ETA:
Linkification-
https://www.law.cornell.edu/uscode/text/8/1325#a
I don't disagree with your analysis. I disagree with your semantics.
Being here "unlawfully" vs. "Illegal" is 6 of one, half dozen of the other. If someone said that a person who "overstayed" entered the country illegally, that would be wrong. However, for someone to say that it is illegal for them to remain in the country, that's accurate.
Further, I think we can agree that "illegal", believe it or not is a general term that means that it is....not legal. "Illegal" may be civil, regulatory, administrative or criminal (or other). It need not mean "criminal" alone.
...but back to the issue at hand. I think it would be a bad idea to criminalize "tipping off" someone on immigration enforcement, but I would fully endorse the removal of specific federal money from local governments that did this.