I feel like you're taking the wrong conclusion here. Perhaps modern society and guns being widely accessible don't mix. Other countries took measures when the problem became apparent, the US didn't.
> other countries don't have 2nd amendment in constitution
Changes to the constitution can and do happen. And it's kind of beside the point anyway because a degree of gun control already exists in the US without being in conflict with the constitution.
> US doesn't pretend to be the same as all the other countries
Clearly. You're also the only one where this is such a problem.
You're 100% correct - changes to the constitution can happen (and have happened). It's not beside the point because any additional controls have to be weighed in the context of the 2nd amendment (as it is written and interpreted today).
The United States has more individual freedoms than most (if not all) countries. The downside of those freedoms is when individuals use their free will for evil purposes.
