You'll note that, yes the US has a higher violent crime rate, but other crime rates are higher - some far higher (drug offenses, for example, are 327 times higher in the UK; total crime victims is 25% higher in the UK, etc).
So certain types of crime rates are lower - even considerably lower - than the US. But other types of crime rates are higher - even considerably higher - than the US.
I’m not following the logic - are you implying police with guns are intimidating, which is the only effective way to stop crime? There are many countries that counter that multiple ways. Look at the militarized police in Central American countries that are 10x more intimidating but much less effective.
I think they are saying that part of the calculation a person makes before committing a crime is what is the likelihood that I am caught or seriously injured. In a society that outlaws citizens having guns the chances of serious injury are much smaller than one where say 20% have a weapon. To the extent that CCTV Cameras increase the likelihood of being caught they have the same deterrent effect of knowing that there is a 20% chance your victim is able to defend themselves.