Well, nobody in New England is treating this as just another routine happens-all-the-time shooting.
I never found the permissive gun laws in Maine particularly objectionable. The state has huge boreal forest wildernesses, a sustainable hunting culture, and to be frank, plenty of places where people live half an hour or more (sometimes much more) from the nearest cop. I don't live there, but if I wanted to, I would expect to participate at least passively in that culture, not expect everyone to change to make me feel more comfortable. Maine is one of only two states in the US with a homicide rate (till yesterday, at least) lower than Massachusetts', where we have far more restrictive gun laws. I'm not inclined to tell Maine, "told ya you were doing it wrong all this time!"
The issue in this case is guns+mental illness (not street crime, drugs, racism, politics, training, or the specific features of the gun). The mental illness was known about and feared by locals who knew the shooter. That should have resulted in the man no longer possessing any firearms (nor being in or employed by the military) but there's no system for making that happen reliably. Nor even much foundation for establishing such a system. You can't revoke a permit that was never required in the first place.
We'll see what changes, if any, the people of Maine demand in the aftermath. I'm not seeing how anyone else's opinion is relevant.