People who know about laws and marriage. If a U.S. citizen marries an illegal immigrant the U.S citizen can be deprived of its own rights?

Lose US citizenship: No.

Go to prison for marriage visa fraud: Yes.

You can get time in federal prison or a fine for aiding abetting an illegal.

The marriage alone isn't any kind of fraud. It's just when the migrant goes home for processing and the US citizen files the petition that they might be suspected of fraud. The primary risk is prison and a criminal record that'll make life difficult.

If the only reason for the marriage was to legalize the illegal (which by the way marriage does not automatically do) then the US citizen is guilty of visa fraud and could face jail time but they would not lose citizenship.
No marriage automatically gives citizenship, they must still be legal residents for the required length of time and need to pass the tests for naturalization

Penalty for marriage fraud is 5 years in prison (can be up to 10 yrs depending on charges) PLUS $250,000 fine.

There is NO way to legalize any illegal alien, not even marriage. If you marry an illegal alien, that person must return to their country of citizenship. They will be barred from entry (typically 10 yrs, but permanently if they have committed any crime). After they complete bar to reentry, if the marriage continues to be valid, you could then file a petition for a spouse visa. However, that person's record of lawbreaking will always be against them.

Your illegal alien spouse can apply for your immigration to that country after returning home. You can live together there. If you do not live together as husband & wife during the illegal alien's bar to reentry, it will be very difficult to prove a valid, ongoing, enduring & committed marital relationship.

Do you want to spend several years in prison? Or do you want to go live in that illegal alien's country for a decade or so before you MIGHT qualify to sponsor them for a spouse visa?

It is not possible to marry someone for citizenship purposes with the exception of Morocco, where the WIFE of a citizen obtains the right to naturalize after 2 years of marriage. Someone could marry the President of the United States (once he's divorced again), and that still wouldn't make her a U.S. citizen nor a man.

But if a U.S. citizen enters in a fraudulent marriage to allow a foreigner to obtain immigration benefits to the United States (Green Card), that's rewarded with up to 5 years in prison and up to $250,000 in fines.

"U.S. citizen marries an illegal immigrant for citizenship purposes" then not only has the US citizen committed visa fraud and can go to prison for that, they are also very uneducated as people do not get citizenship just because they marry