You talked about not painting both sides with a broad brush. The difference you're overlooking is that the left wing establishment HAS associated itself with the groups that caused violence. Yes, there are violent people on the radical right but they don't get endorsed by conservatives.
You talk about silence from conservatives regarding right wing violence, and it seems to me that you're just tuned in somewhere else and didn't get the memo. BTW regarding the shooting of Mr. Castille, DANA LOESCH was critical of the police officer (but you have to listen to her not NPR in order to hear that).
You talk about "blowing a few incidents out of proportion". Yes, most of the protesters are peaceful but antifa's violence and vandalism has become routine in places like portland and seattle. As for BLM, how many riots have there been and how many LEO's have been ambushed and murdered? More than "a few incidents". Again, the difference is that the left has excused if not embraced these groups whereas conservatives have no time for white supremacists.
As for inclusivity like taking non gun owners to the range as you suggested, the NRA has been pushing a grass roots mentor program to do exactly that.
Do you remember how 'W' Bush wouldn't respond to all the hyperbolic accusations against him? What's being said about Trump sounds very similar. My point is that neither issues or Trump spending time on twitter to talk back, has much to do with what's said about him...and his family. Given how polarized the country is/was, I think it's better use of the NRA's ad funds to reach out to those who voted "Trump"--or against clinton--than to run milquetoast outreach ads to people who aren't going to change how they vote--typically anti 2A.
Which left wing establishment are we talking about there? The DNC? BLM? Bernie Sanders? I'm not sure I recall Hillary Clinton advocating for violent riots during the campaign, but then again, I tended to tune out her BS, so I admit I could have missed it.
As to Dana Loesch and the NRA finally commenting on the Castille case, you'd have a lot more credibility on that statement if 1) they didn't issue an extremely mealy-mouthed "it was regrettable" non-statement and 2) they didn't wait until more than a calendar year after the shooting and after the trial was completed. I don't recall the NRA wanting to wait until all the facts were out before they castigated any left wing or Radical Islamic actions.