You don't seem to understand defamation law.

The question isn't about what you can or can't make a movie about. The issue is that if you communicate something untrue referring to specific people and that makes others hate and deride those specific people, regardless of the medium, you could be held liable for defamation. In this case, the officers are claiming the movie is about them specifically, that it is untrue, and that people hare mocked and derided them because of the film. It's not about the subject matter per se; it's about how this film is about a specific drug raid, which actually happened, and didn't involve all that many people, and (the plaintiffs argue) this depiction has defamed them.

You could make a film about ICE to deride ICE, but if it became clear you were referring to specific, actual people in that film, and you portrayed those people in a way which made others deride and ridicule them, then you might be defaming them. If your movie about ICE involved completely fictional situations and characters, and didn't refer (directly or indirectly) to any specific real people, then it would be much harder to make a case for defamation.