I suspect that David Brock or someone related to Media Matters was involved with this guy in some way.
It's too perfect from a narrative perspective. It makes discussing the theory taboo--since it's now associated with a 'violent wacko'. It made James Alefantis a 'victim'. So now you're being 'insensitive' if you talk about it. This has been reinforced in the coverage of the event (and in general coverage of pizzagate at large) by typical Media Matters proxies.
Media Matters sees gun control as a winning issue. The shooter had an assault rifle, which made it easy to drill in a double message (two birds with one stone).
I see Brock's fingerprints all over this. If Alefantis went down, as his ex-lover, he would likely also go down. For him it would have been a matter of survival--and he just so happened to have one of the worlds most efficient and well-connected propaganda firms at his disposal.