There may be other explanations for it, but European countries do have lower murder rates than the US. So pro-gun control makes the claim that the US has the highest murder rate of any 'developed' country, which is true, but they blame it on the availability of guns alone.
European countries have lower murder rates than the US: true.
Pro-gun control make the claim that the US has the highest murder rate of any developed country: true.
Absolutely none of this is true.
European countries have lower murder rates than the US: true.
Pro-gun control make the claim that the US has the highest murder rate of any developed country: true.