A lot of people are influenced by alt-right news (Fox News, Newsmax, OAN) who keep repeating the false claim that undocumented immigrants are mostly gangsters and violent criminals.

Trump said, regarding the first deportation flight:

Three hundred people sitting on a plane. Every single one of them is either a murderer, a drug lord, a kingpin, the head of the mob, or a gang member

Yet none of those deportees had any criminal conviction in either country (according to Newsweek, a slightly-right news source).