I'd also be interested to read the same article written from the opposite perspective (i.e."Why mass shootings convince non-gun owners to support gun control") with an equally reasoned explanation by a "conservative" of the "liberal" mindset (liberal and conservative as defined in the article).
Well, a simple explanation is just turning the article around:
Opposing firearm ownership is an issue of tribal solidarity, a show of support for Obama, the left, and the changes they represent.
You can tell people who oppose firearm ownership about the higher crime and murder rates in cities like Chicago and Philadelphia, which have the strongest restrictions, the most impositions on other freedoms, and the hostility to people in other jurisdictions, until you are blue in the face but they simply won't listen.
You can cite the higher popular support, and increased sales to new owners, every time the crime rate surges and there is more talk of "regulation". You can point out that, in point of fact, people who support "regulations" invariably also insist on confiscation - just like happened in Australia.
You can also point out just how many mass shootings occur in "gun free zones" compared to "ordinary" places, as well as the lower death rate in such instances when an armed bystander intervenes rather than waiting for the police.
And you can point out that firearm restrictions have always been used as a tool of oppression of minority groups and never as a means of empowering them.
Ultimately of course, the reason mass shootings encourage people who support firearm prohibition in their beliefs and advocacy is because such people are already predisposed to reject personal responsibility, believe that the "authorities" can protect them and provide all of their needs, and that since they know they are being reasonable, by definition anyone who disagrees must be unreasonable without any further argument being needed. And of course, such people are a threat to them that the government must protect them from, by of course disarming them.
None of this matters, because it has "become" an issue of tribal identity, opposing Bush (who isn't particularly liked by conservatives anyway), and the right, and the stability and rule of law they represent.
Which of course leads to the realizing that the article doesn't actually have a reasoned argument. It is just "they're opposed to us politically so they won't listen no matter what!" Sprinkled into that are pretenses of personality "research", that even the author has to admit is essentially useless, likely because he recognizes there is just as much out there to indict members of his tribe for their knee-jerk acceptance of firearm prohibition.