Increased/easier lethality for both. It's easier to kill yourself with a gun than anything else, so a strong impulse can cause irreversible death much quicker and more reliably than going to find a bridge, attempting to poison yourself, or attempting to hang yourself. Those options are all slower, scarier, and take more time in which you can change your mind or be rescued. Domestic violence. If somebody sees red and beats up their wife, there's more chances for the wife to leave him or for this to serve as a wake-up call for them both than if a gun is available. With no gun available, even if he would shoot her, he can't. A knife or strangulation are much more raw, and less reliable ways to kill, and again with the slower, scarier, and takes more time usually. The hill to climb to achieve death is higher, and in the meantime something is much more likely to happen to avoid death than if a gun is used. Drunk roommates get into a fight - without a gun somebody gets beat up, with a gun somebody is more likely to die.