Willie Wonka reads tweets.

Because the best way to justify one's political opinions is to shoot them, right?

Political opinion has nothing to do with it. The lady that tweeted that first statement was attempting a generalization and/or guilt-by-association fallacy which wasn't even based in reality since none of the mass shooters were NRA members. Willie's retort was also a generalization and/or guilt by association fallacy that was based on reality because several if not most of the mass shooters have been left leaning or registered democrats.
I thought it was a good retort and should be shared.

Where did you hear that most of the mass shooters were left leaning? The only one I can imagine being at all leftwing is the shooter from Texas.

Which Texas shooter? U of T, Luby's restaurant, Ft. Hood, or Sutherland Springs?

Well, instead of going by what Snopes says or what we may read in some meme, I look at the lifestyle of the person who commits a crime, I try to acquire information about them before most of it is scrubbed from the internet.

Hodgkinson was a Sanders supporter and posted anti-Trump vitriol on his FB.

Sutherland Springs shooter was a vitriolic anti-theist who constantly posted about how religious people were stupid. I do believe it was the Democratic party that voted to remove God from their party platform (I think but am not sure, that they had to re-write it again to put God's name back in because of backlash.) It seems like he would have fit in better there.

Vegas shooter was an incessant gambler, that lifestyle seems to be one that a left leaning person would live since most "conservatives" say they are against legalized gambling.

Those are just the last few I could think of, their lifestyles/behavior seems to lean toward the left even if they were not political at all.

Fort Hood shooter was a Muslim (although officially the 13 people he murdered and 30+ he wounded were classified by the Obama admin. as "workplace" violence.) Being a Muslim doesn't necessarily make him left or right leaning.

The Luby's restaurant shooter had been fired from jobs for drug use. That doesn't necessarily make him left or right either.

Charles Whitman shot up University of Texas, he was a "former" marine, we could speculate about what motive, if any he had, but true facts about him are probably only available at the library in older edition books.

I did see an article recently describing about how many atheists can actually be quite bigoted, fighting each other because of differentiating ideas, similar to most organized religions. Richard Spencer is an example of an atheist who has radical disagreements with liberals.

I don't know when this tweet was tweeted either.
I do know that many former mass shooters were on the left at least if not Democrats or full blown Leftist (I see a difference between normal people on the left-Democrats and Leftists.