These "False flag to take our guns away!" theories don't make any sense. We have had several such shootings here in the USA, and none of them has had the effect of getting guns taken away. The gun lobby always argues that if everyone had guns, these shootings would not happen.
If the government really perpetrated a psy op to seize guns, there would be a shooter who opens fire, while a few gun-carrying citizens fire back and kill several innocent bystanders but fail to stop the shooter. Otherwise it is the same thing we have seen before that did not result in martial law or whatever nonsense they fantasize about.
Believe it or not, there is a series of fiction books based on the premise that a false flag mass killing using a semi-auto causes the government to ban firearms, and the Republic then falls, only to be partially rescued from the liberals, lesbians, aztlan invaders and gun grabbers.
http://www.enemiesforeignanddomestic.com/author.htm
On the second bolded point, there is a certain amount of truth in that statement.
Generally speaking, with some singular exceptions, spree shooters do not bring themselves into venues with armed victims - police stations (some exceptions in the 1960's - 1970's, one in the 1980's) as part of political terrorism, Military facilities with armed troops (Ft Hood doesn't qualify, the grenade attack in Kuwait does) Gun shops (burglaries yes, armed robberies, not so successful) Gun Shows (negligent discharge yes, criminal shootings no) and shooting ranges - suicides yes, a deranged woman shooting her son yes, but criminals, not so much or good.
Now does that transfer to the public at large, it's not clear, but it's not entirely unreasonable to suppose that bad actors that are not suicidal attempt to pick unarmed victims in areas unlikely to have armed, aware and trained individuals.