I can't say that I agree, but I certainly get where you're coming from. You explained why you feel the way you do and that's all one can really ask. So, c'mon, guys. Don't downvote just because you disagree. All opinions are equal, are they not? In fact, the ones with a different point of view are often more important than the ones that confirm your own believes. So don't be a dick, OK?
With that said, here's my take on the matter: I think it's sad that this more or less marked the end of Jon trying to communicate with fans on social media. He went quiet for a while after Game Grumps ended, but he was just getting back on Twitter, so that really sucked. This collection of tweets doesn't show you the vast amount of shit Jon got sent to him from SJW's as a result; calling him names, disliking his videos... it was a bad scene. It also doesn't show the shit that we, the fans, sent to the guy he confronted, either. There were no winners here and it's hard to defend anyone's actions.
Jon's clearly very passionate about freedom of speech and anti-political correctness. It makes sense that he replied to this tweet as oppose to simply ignoring it. Was it wrong to call him retarded? Well, that's the problem, isn't it? That it's up for interpretation and that there really isn't a clear answer? But it's Jon's style of humor. I guess he might have thought that his fans were on board with it. It's hard to tell whether or not the person perceived it as an insult or just accepted it as Jon being Jon. The SJW's who later attacked Jon certainly took it as an unprovoked insult, though, speaking for both Jon and the person he called retarded on the matter (which, to me, is pretty much the greatest insult of all). By doing do, they made Ben into a victim, not Jon. He was clearly capable of standing up for himself and his beliefs; they both were. I side with Jon on the matter of political correctness, but it's hard for me to take this as anything but a regular conversation.
Tl;dr: The event itself wasn't the bad part, but rather what happened as a result of it (not featured in the picture). Don't take things out of context.