the shooter did not have psychosis, he wouldn't of been able to effectively do what he did and plan it

Well I disagree on this, psychotic doesn't mean 'all out crazy' I'm drunk but that's not how pychosis works, they can be very 'normal'

And you want a government monopoly on firearms, the biggest mass murderers of all time?

That goes for all militia, a government is the one with the overpower (money, weapons, sexual interests) aka the one who has governance.

whilst writing a well-written manifesto, that he probably did not write.

I've read a bit and it's not well written and it's absurd to think he wrote that 'just before' doing it

Even if he did, doesn't mean he was right in anyway.

And in the states people with guns stop bad people with guns all the time.

'bad people with guns'

QED