Your argument is a non sequitur.
The legal fact of the matter is that simply being a U.S. citizen does not automatically give you the right to vote in a Federal election and being an immigrant and being a citizen are two separate issues under the law.
A convicted felon that is a U.S. citizen does not have the right to vote.
A 17 year old U.S. Marine that is a U.S. citizen does not have the right to vote.
If you advise that 17 year old U.S. Marine that, "If you are a citizen of the United States, we ask that you participate in the democratic process of voting" you are advising the 17 year old U.S. Marine to commit a crime.
An immigrant can become a U.S. citizen but the fact that he is an immigrant rather than native born is a point of law that even the Constitution addresses in Article II, Section 1 as a disqualification for ever being President of the United States.
Under U.S. law, the rights of native-born U.S. citizens and immigrant U.S. citizens differ precisely because you can be both an immigrant and a citizen.
"U.S. citizen" and "individual entitled to vote" are not legally synonomous phrases.
In addition, "citizen" and "immigrant" are not legal antonyms.
This man was threatening U.S. citizens who were immigrants about "jail time" and "deportation" if they voted in a Federal election in violation of the intimidation provisions of the Voting Rights Act.
If you ever try to intimidate a U.S. citizen from exercising a civil right guranteed under law by threatening "jail time" or "deportation" or whatever other threat you want to throw in, you had better ensure that your legal wording and your legal logic is impeccable and that you can carry out that threat in a court of law EXACTLY as you phrased it.
If your threats can be excused only by having your attorney explain to the Judge, "what my client actually meant to say", you have a good chance of ending up with jail time yourself.