On what grounds? The email was sent to law enforcement officials, and the plaintiff acknowledged having attacked the photographer; the act this poster represents.
If I take a picture of you and caption it that you are a child abuser and limit my distribution to law enforcement, you would say that is okay? If you got mad at me for it and you hit me, then that would make my action okay?
This has nothing to do with first amendment rights. We are both free to defame anyone we please. We just have to pay the penalty.
The caption was false and clearly was intended to defame the men in it. I’m sure the creator could have found pictures of actual illegal alien criminals to make his point but using someone who had no such record was wrong.