Why should you be allowed to decide if people can do something? You don't get to control 334 million peoples' actions and interests and neither do I.
As long as the parameters are legal and the results don't harm anyone on their own, the problem isn't with the things, it's people who cause the problems.
If someone finds a way to sharpen knives better than anyone in human history, should they be denied the opportunity? As long as they aren't promoting violence, I think not but since you want gun control, look at the rest of the World to see that they have big problems with knife attacks-
More than 130 people in Kunming, China, were injured when about ten men and women wielding knives began stabbing others at random
www.smithsonianmag.com