Perfectly reasonable to you, maybe. The law isn't something that we can bend and change on a whim of opinions, it's something that is drafted, debated, and eventually voted on by the representatives. It may seem reasonable to you at present, and may seem reasonable for the people of Utah to change the law if this event sparks some social discussion, but one cannot assume what is reasonable to you is reasonable to the rest of us and just make a claim that the law should bend for your reason. Because it's your reasoning, not necessary everyone else's.
Let's not forget that everyone interprets the law differently, and that something reasonable to you is not necessarily reasonable to me. That's the entire reason why laws exist: we don't all agree on what's ethical or logical or reasonable, but we must obey a set of statues (this goes for police officers, too, in this case). It may seem illogical to not disarm attendees to you, but it is the law.. And subject to change through legal means, but not on a whim of some present opinions.