I just wish I ever heard one good argument from anyone on pro gun camp. Ever. It's always the same, tired, discredited bullshit. Niall is now even reduced to 'WELL SOMETHING IS BETTER THAN NOTHING" which is about one notch above 'nyah-nyah'.
Here would be a few legitimate arguments that actually address the criticisms of your position:
1) OK, so yes, terrorists will probably still go through with their plans even if gun control exists, but its possible that gun control in one jurisdiction at least changes the target to a jurisdiction without gun control, because its easier there - at least if both jurisdictions are islands like Australia / New Zealand. So while there may be an attack either way, at least the community which enacts gun control might not be the victims.
OR
2) Gun control might not be able to stop someone from committing violence with a gun, but making them contraband at least makes the transport and sale of guns more risky, and gives police reason to arrest those found transporting a gun/flaunting the law if they are able to identify them prior to attacking someone.
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At least those arguments make a little bit of sense and aren't completely contradictory to logic or observed history.