You might need to start by more fully explaining exactly what you mean when you say you are "against guns." Do you mean that all guns should be destroyed? Are you saying that private ownership of guns should be against the law but it's OK for police and the military to have them? Are you distinguishing between different types of guns, allowing handguns but prohibiting rifles for example? Would you allow hunters to continue to have guns for their sport?
If there were no guns, the risk of accidental shootings would be reduced and criminal activity involving firearms would be lessened. You should be able to find statistics to illustrate the number of fatalities and injuries caused by guns, depending on how you are narrowing your definition.
The Second Amendment to the Constitution guarantees private citizens the "right to bear arms." Exactly what that phrase means has been interpreted and reinterpreted over the years, but it certainly doesn't allow for the complete banishment of all guns. The military forces and law enforcement officials would argue that guns are a necessary part of the equipment needed for their jobs.