Times when it is alright to shoot someone:
Is your life in immediate peril?
Is someone actively trying to kill you, assault you, rape you, rob you, do you serious harm, or do any of these things to someone you are currently in the presence of?
Are you a police officer/soldier/peace officer on active duty and in that moment feel that it is a necessity?
If you answered yes to any of these questions then it is probably alright to shoot someone.
Times when it is not alright to shoot someone:
When someone doesn't agree with you.
When someone does something you don't agree with.
When someone is a different race/religion/sex/sexual orientation/nationality/profession than you.
When someone supports a political or ideological stance that you oppose.
It is never alright to open fire on hospitals, schools, malls, highways, offices, or any other public locations if you are not in an active war zone. News flash, there is not an active war zone in America.
America is plagued with domestic terrorists. Don't agree with me? Well here let me help you a little.
Terrorism, as defined by Merriam Webster dictionary (and this is the 'for kids' entry so that it is in the simplest terms): the use of terror as a means of achieving a goal.
Domestic, again as defined by the for kids section of Merriam Webster dictionary: of, relating to, made in, or done in one's own country.
Shooting a bunch of kids, clinic workers, or innocent bystanders in American suburbs pretty well fits these definitions to a T. Also consider that these are not isolated incidents. This stuff happens on a weekly basis. Police officers shot because people think that cops hate black people. Black people shot because people think they hate police officers. Clinic workers shot because they are pro choice. Muslims shot because they are not Christian. Children shot because someone thought it would make a point.
Well you are right, these acts do make a point by causing panic and terror. These acts don't rally support for the cause, it simply causes reactionary violence. It puts everyone on edge, makes them afraid to leave the house, and in turn causes more hate. It is an endless cycle of violence and hate.
Banning guns is not the answer. Just because guns are not legal does not mean people will stop shooting people. It simply means that the black market for guns will be stronger than it already is. People will still feel the need to own guns to protect themselves and will find a way to get them. People who want to shoot up a school campus will find a way to do it whether the materials are legal or not.
What is the solution to this? Fix your attitude. Never ever condone this sort of violence. Never say words like "They deserved it." because they certainly didn't. Stop hating people who think or are different than you. Stop teaching your children to hate. Accept that you are not the only person in the world and your views and lifestyle are not the only ones out there.
That is how we start to fix this. Remember that ALL lives matter. Stop viewing people as the enemy and treat them as your neighbor and a fellow human being who deserves the same respect and freedom you expect to have. Do not continue to divide yourself because of where you were born, who your parents were, where you do or don't pray, what you eat, or who you are voting for.
Be a good person. Don't be jackasses. Don't sit by quietly and let this happen. Don't just post snarky passive aggressive memes to Facebook, or change your profile picture to something patriotic, or blame a politician or the media (hell stop listening to the media altogether), or shake your head and go on about your day. This accomplishes nothing.
Do something positive. Start a positive dialogue with someone who is different than you. Donate your time to helping others. Give blood. Give money. Give canned goods. Give a smile. Be kind. Be good. Be the best you that you can be. If we all did that then maybe the idea of shooting a stranger wouldn't be something people thought would be a good idea.
I feel like I have said all of this before, but apparently it needs to be said again, so I will continue to say it until it does not need to be said again.
Be good. Stop hating. Be tolerant.