Should Omar Mateen have been legally allowed to buy a gun on June 10, 2016?

[Mr. Reactionary]

He would not have been able to had it not have been for a bill the House Republicans blocked.

Has it been confirmed that he was on the no-fly list? Or the terror watchlist? Because those aren't the same thing. I said no though, because it sounds like he was guilty of misdemeanor domestic assault which results in gun restrictions following a conviction.

[Mr. Reactionary]

The second amendment was never interpreted to guarantee an individual right to a firearm until Antonin Scalia invented one in 2008.

Ummm ... no. From St. George Tucker and Justice Story in the early days to post 14th Amendment cases like Cruickshank, jurists have clearly accepted the first 9 amendments (including that pesky 2nd) as being individual rights. Pre-14th Amendment the bill of rights only protected against Fed action so there clearly was not need for much interpretation for most of our history. Does that mean its fair for me to say that the 3rd Amendment has never been interpreted to guarantee an individual right to keep soldiers out of your house in peacetime, simply because there has never been a Supreme Court case about it? Yeah, in the 1930s the Court made a dumb decision in Miller because only the government got to brief, but even then its not like anyone seriously entertained the idea that "the right of the people" meant something else until recently as well. The Court corrects bad decisions all the time (Brown v. Board), and the decision in Heller does not even undermine the holding in Miller.

[Mr. Reactionary]

"According to reports, the alleged gunman in Orlando, Omar Mateen, purchased an AR-type rifle and a 9mm semiautomatic pistol legally despite the fact he had been questioned twice by the FBI. There was no open investigation at the time he bought the guns. Mateen was not on the watch list at the time and it is not clear that this bill would have prevented him from purchasing guns."

http://talkingpointsmemo.com/dc/dems-renew-push-to-stop-people-on-no-fly-list-from-buying-guns

[Mr. Reactionary]

Many acts that are perfectly fitting the description of "domestic terrorism" are either overlooked, but described as simple murders/shootings.

If the Columbine shooting (any of recent school shootings) was being perpetrated by a Muslim, media would instantly call it a terrorist act, rather than "just" a "school shooting".

No, if the Columbine shooters had a political agenda with their shooting they would have been called terrorists. Terrorism requires a political motive, such as the Charleston church shooting, oklahoma city, orlando, etc.  (Oops, looks like 2 of those were done by white guys)

Stop moving goalposts to fit your agenda.

What goalposts??

About what "you" consider terrorism.

[Mr. Reactionary]

While other dictionnaries only mention the terror part, not the political one. The very meaning of terrorism is subject to a debate, not everyone agrees with your view.

Could you cite to one to make me feel better. When I googled definition of terrorism I'm literally only seeing definitions which include the political motive requirement on the first several pages.