How can I explain my confusion?

I got a huge shock when I watched a trailer of a movie for kids.
The title is POKEMON which based on one of the famous Japanese animation. A protagonist is a teenage boy aged 15 or 16. One day, he accidentally found a monster in his room. (I checked IMDb’s Storyline, thus I know he is a 21-year-old, however, the situation didn’t make a difference for me…My surprise doesn’t decline.)
The monster can speak English, but nobody understands it can speak, the protagonist is the one only who can. I was surprised in the scene where they met in the boy’s room. When he entered his room, he recognized a strange noise. Thus he immediately stands by to shoot his own gun!!
I was so surprised. It’s an unbelievable situation in a Japanese movie for kids. I know it’s just a fiction movie, but…the movie makers didn’t have doubt that foreign people who watched it will easily accept this scene. In my opinion, it is horrible. It simply shows about US’s social problem. Japan is proud of the lowest crime rate in the world. It is because there is a strict rule to get a gun. It’s an impossible thing that kids or young adults hold their own gun in their room in Japan!! (Even adults are also difficult to get a certificate of guns. )I believe it’s an abnormal society that people easily buy weapons which can hurt other lives. How can I explain why I got surprised so much? Does this way is understandable for others? I guess almost all Japanese feel the same as me, but I’m not sure with other countries’ people who have a different culture from Japan to feel similar to my opinion. Maybe I’m a super conservative about using a weapon.