Allowing police to search homes without warrant or probable cause, to torture suspects, to imprison suspects for life without trial, to set up ID and X-ray checkpoints on city streets, etc. would probably reduce violent crime by “civilians” as well. But the result would be a state of affairs that would be *worse* than violent crime.
I’m sure China has very little violent crime by civilians...but when you count violent crime by the government, they have almost certainly murdered more people since WW2 than the rest of the planet combined.
The Bill of Rights is there for a reason. Yes, pragmatic arguments are very effective against the stupidest gun control proposals, like banning certain rifle handgrip shapes (“assault weapons”), trying to ban and confiscate magazines with less capacity than a 1777 Girandoni or an 1861 Henry, or limiting carry licensure to the rich and famous. But infringement on protected civil liberties that didn’t fail pragmatic tests would not automatically be ok, because civil liberties are foundational to a just society.