The probability of you being killed by a terrorist or a Muslim in the US is tiny compared to your chances of being killed by a native born or white (assuming you're white). The percentages are so small, it makes such an outsized concern obviously racist because from a rational risk assessment point of view, it changes nothing.
>So what? They don't have some sort of magical automatic right to be here just because one of their relatives is.
We have generally held it is good policy to keep families together. And the times when it was not allowed (e.g. Chinese Exclusion Act) were specifically done for RACIST purposes, not rational ones. Tons of Chinese men were prevented from being reunited with their wives because of that, and still more single ones were prevented from marrying locals by anti-miscegenation laws.
These kinds of attitudes are basically the ones that allow you to be manipulated by political parties and have your attention diverted from real issues. Xenophobia works unfortunately, as studies and social experiments from the 60s and 70s show, blaming woes on "the other" is a tried and true tactic. You can take tiny issues related to foreigners or other tribes and blow them up so large they dominate the discussion.
Immigration and terrorism are not the largest issues facing this country, yet they completely dominated the election.