Chance, no one is disregarding the magnitude of the horror the defendants are accused of perpetrating or the pain and destruction it caused to the victims.
However, when it comes time for a trial of the accused in this, or any crime, it is about seeing that justice is done and that the guilty are punished. For better or worse, we have set up a process in this country, guaranteed by the US Constitution, that provides every accused with due process of the law. It's an adversarial system, with rules of procedure and evidence that seek to eliminate emotion. For example, there is a rule of evidence that permits the judge to exclude relevant evidence "if its probative value is substantially outweighed by the danger of unfair prejudice . . .." A judge is not permitted to make rulings based on his perception that the defendants are horrible people accused of a heinous crime. Justice cannot be done if the weight of the evidence is tainted by efforts of prosecutors or defense attorneys to introduce evidence that inflames the jury against the accused or a witness against the accused. Keep in mind, sometimes the prosecution relies on some pretty unsavory characters to prove a case. Evidence of a witness' sliminess may be minimally relevant, but it may not proper to admit it at trial in order to prejudice a jury weighing his testimony.
The protections in our system guarantee that every person accused of a crime enjoys the presumption of innocence. This isn't something 20th Century liberals thought up. It's origins go back to the Roman Empire, is something virtually every democracy has incorporated into their law, and which is understood to be enshrined in our own constitution through the 5th, 6th and 14th amendments.
So, the first responder whose article you cited is justifiably angry about what he and his fellow victims suffered on 9/11. Witnessing any trial can be an unpleasant, and at times enraging, experience. But anger and emotion is no basis to operate a system of justice. I'm no different than anyone else. If I read about a horrible crime in the newspaper or see it reported on the news, my initial impulse is that I'd like to take a baseball bat to the people who committed the crime. I myself have been the victim of a violent crime. It was the first time in my life I thought I might die and the first time I realized that I had the capacity to kill someone, so visceral was my rage at the people who perpetrated the crime against me. Despite my personal experience with being a crime victim, and having friends who had also been victims of violent crime, I still strongly support the protections of our system that are supposed to guarantee the due process of law.