"I don't think I could enact violence."
Just say that. Don't moralize about weapon ownership or downplay very real threats.
"I'm not mentally well enough to have one."
A some point the threat of violence from fascists will exceed the threat of self-harm. Only you know when that will be, but it may be sooner than you expect.
"Guns are scary."
The future is scary. It doesn't mean we won't have to face it.