I'll go a bit deeper.
You cannot reason with the unreasonable.
People who think guns are evil will keep on believing that no matter what evidence you show them. Offer to take them shooting, and let them experience it first hand, and almost immediately you can watch them questioning their beliefs on guns.
One of the best things is taking an arrogant anti-gunner who thinks he knows all about guns to the range, and seeing the smile on their face within minutes of firing that "evil black piece of metal." It doesn't always work, but it's FAR more effective than arguing and trying to speak a trump card to them. The ultimate trump card is giving them trigger time...and you don't have to speak a word.