I'm starting to have violent fantasies at night, most probably because I'm anxious about what my grades are gonna be in my school leaving exam. That the fantasies center around cathartic violence (destroying stuff, smashing windows) probably means I subconsciously believe that violence is the solution to my problems, but that's something for another day.
...d...doesn't everyone do this?
Well now I'm mildly concerned.
Hell if I know. All I know is that Mom tells me that violence is not the answer. I'm inclined to agree with her, but I have nothing to back it up. Doesn't stop me from massacring whole villages in, say, DF, though.
AFAIK those so called "violent fantasies" are quite common in teenagers (something about puberty) and don't mean much as long as you don't act them out. Still, if you feel like you can't control them or even if you are simply curious to learn more about them you could always contact an expert. There is no shame in wanting to understand/better yourself
On the more philosophical stuff and since you expressed some doubts about the whole "violence is not the answer" thing, I think that your mother is half correct. A lawful court prosecuting a murderer, a person defending their life/property or people protesting against an unjust law are as much expressions of violence as are murder, assault or exploiting a law. The only difference is the purpose behind these actions.
Violence is a tool, one that has been extremely vilified but a tool nonetheless and as such it isn't inherently good or evil. Learning when, how and for what purpose to use violence, is a valuable skill yet people are afraid to teach it in fear of it being misused.