I personally don't think it's making the agents worse, but rather that it's very heavily selecting for very bad people. If you have a job where people can be violent and abusive with little-to-no oversight, you are going to select for people who want to do violent and abusive things. Keep in mind, these people aren't being "drafted" into ICE, they're voluntarily joining, meaning that they had to demonstrate some interest in it.

This doesn't imply that every ICE agent is a terrible person, just like how not every Catholic priest abuses children, but if you create a selection pressure then it isn't surprising when you get what you selected for.

Sample size of one but bear with me; I am an asshole but I am a decidedly non-violent person. I genuinely do not want to commit any form of violence on people. Law enforcement doesn't seem appealing to me because it pays worse than software and I wouldn't view physically attacking people with impunity as a benefit.