Gun and knife crime is an economics issue. Don't see how religion fixes it. El Salvador is pretty much 100% Catholic with huge religious participation. Doesn't really stop them killing each other.
If you were to take an extremely static view what you are saying is true. It’s just not true in the dynamic view and in the long run. Christianity largely got us here, any argument to the contrary is mostly nonsensical stuff about the Greeks who were too childlike and failed.