he FBI and other investigatory services are thinking this dude had another motive, that is hate or mental issues, that drove him to do this.
So the reasons he gave explicitly weren't the reasons? I mean, the guy posted his reasons on social media and called up a reporter. It's not like it was meant it to be some big mystery.
Almost all incidents involving mass murder on this scale was because someone was able to go to a gun store and buy a AR-15 and then go kill as many people as they want.
Not this one. There was no AR-15.
Make an argument if you wish, but demonizing a gun that wasn't even used during the crime is not a serious response.
People in the military are issued these weapons, taught weapon "rules" and these weapons are accounted for.
Other than it looking scary, please explain why this gun is any different than other hunting rifles or handguns that might be used in its place. How many mass shootings will actually be prevented because the shooter will have to go with an alternative? How many lives will be saved because it's not available? I'd wager to say that the answer to both questions is: None.
The reason it's found with some frequency in such shootings isn't because it's particularly deadly, but because it's particularly popular. We're literally making a national political issue about a specific gun because of its success in marketing.