The country obviously has no obligation to give visas to anyone. However, once you are within US jurisdiction (i.e. in the country), you have a suite of Constitutional rights including (unambiguously) 1st Amendment and 5th Amendment rights. So, correct, they definitely cannot be deported without due process. They cannot be deported even with due process for protected speech. They cannot even lose their visas for protected speech. There are a million different reasons the government may decline to give someone a visa or they may revoke one, but "engaging in protected speech" is not one of them.

And yes, yelling "kill all X" during a protest is protected speech in this country, which AFAIK is far beyond what any of these people are alleged to have done.