"the availability of guns is directly related to the number of mass shootings. "

False, you just made that up.

In the UK almost all firearms were banned after a couple of mass shootings and there has not been one since.

How frequent were they prior to that?

The same goes for Australia.

False, they have had mass shootings there and of course studies of their mandatory gun buybacks found that their draconian laws did not cause any reduction in homicides suicides or mass shootings. In fact gun homicide rates in the US fell more than those in Australia following their ban.

Every democratic government has to balance freedom against security.

THERE IT IS! In your sentence, and whenever you hear anyone making that statement the word "balance" really means "take away", every time. Here is America our founders warned us that those who would trade liberty for the illusion of security will have neither. Of course they were right. This shooting was in a gun free zone right? One of the only places in Florida where people cannot defend themselves, is that a coincidence?

And I think that the fact that you can be on a no fly list as a suspected terrorist, yet still have the right to buy and carry a gun to be slightly misaligned priorities.

Indeed, its absurd that we have secret lists of innocent Americans, mostly Muslims, isn't it? Democrats used to rightly oppose the idea of stripping Americans of civil liberties without any due process but then they decided that if gun rights were stripped then they really like the idea of stripping innocent, mostly Muslim people of basic civil liberties in secret and without and due process. Lets think about how you get on their secret lists, its by associating with the wrong people, saying the wrong things or going to the wrong mosque right? Or just having the wrong name right? So essentially exercising your first amendment right should strip you of your 2nd and 5th and 14th amendment rights? Democrats in the house think so, they protested against civil rights.