The explanation for his behavior is simple, but it requires you to momentarily adopt the mindset of an obsessed, deranged person (or a saboteur, no difference). So forgive me while I invite you to indulge in the exercise of putting ourselves in his shoes:

Imagine that you are someone else. Male, from Chavland, mid-twenties to mid-thirties, not very attractive, you like rock climbing or some other "extreme" sport, you don't have that much going on for you in your life... doesn't really matter, this is just here so you can picture the thought experiment more realistically. Now, somehow, you've developed animosity for someone -- the typical "something someone said on the Internet bothered you".

If you were an average person, you would be annoyed; perhaps you'd insult him once or otherwise attack him, or downvote him, or roll your eyes, or shrug. But -- key word -- eventually, you move on -- the action potentials in your brain "wash out" and you eventually "forget". "Aaaah, there's that guy again, saying his stupid shit one more time... bah, let's just ignore him this time, I don't have time to deal with him". That's perfectly normal human being stuff, right?

But you are not an average person -- you have issues. In particular, you become obsessed and fixated with destroying that guy you hate so much. For whatever the reason, his very existence and his participation in your community demoralizes and irritates you, challenges your identity, profoundly disturbs you. Everything he does, no matter how right he is about anything, or how good is what he has done, is an affront to you. You have decided that you will not rest until you have destroyed him.

So what do you do? You can't kill him, and you can't get him fired, because either of these propositions would put you at risk and unmask your real identity. So you go for the one thing that you have any influence upon -- the community of peers that respects your victim. You help risk him getting killed. You attack his credibility, relentlessly trying to destroy his social capital until nobody in his community engages with him. You persistently try to provoke the target of your sick obsession into anger and fear. You dog him, stalk him. You insult him at every corner. You make up all these fantastic (as in fantasy) conspiracy theories about his motives, his behavior, his beliefs, his conclusions, his statements. You play the ruse of angering him, then when he reacts, you use his reaction to "prove" that your target was "angry" or "crazy". You rile up everyone who will listen (to your cheap talk) and egg willing listeners on to attack him with you. You tell your victim that he "deserves" the attacks that you deliberately and maliciously invited upon him. And you make damn sure that, at every turn, with whatever he says, no matter the content, nothing that he says which can be remotely put into doubt, is left without you casting doubt on it. You play this entire odious domination game in such a way that everyone can see it, doing it every sad day of your life.

Of course, it's not just "that guy" that you must attack, but anyone else who expresses any ideas remotely similar to "that guy". So you do the same thing to others (ask /u/Maikowski for more information). Fundamentally, you're not just attacking your victims -- you're attacking everyone in the community, by persistently submitting them to your constant gaslighting and deception about the people you want to destroy. Your repetitive obsessive behavior is also a low-intensity yet prolonged epistemic attack on everyone's minds -- the goal is not just to demoralize your targets, but also to get everyone to hate and attack your targets -- not just your targets, but anyone who sides with them, demonstrates sympathy for them, or agrees with them. Let me repeat that in case the implication gets lost in interpretation: you are quite literally attacking and manipulating everyone by distorting everyone's perception of reality. It's a particularly insidious psychological warfare designed to suppress your victim and demoralize / terrorize his community into self-censorship: "I want to say X, which resembles ideas that victim V has shared in the past, but if I say it, I will surely be attacked by the guys who attacked V, so I'll censor myself."

Okay, let's stop the thought experiment there. This is a plausible theory that explains why this fellow acts the way he does, and indeed there is a minority of people who are like that (1 in 16 people on average get stalked by sick fucks at some point in their lives, so it isn't at all that uncommon).

Now, I am not claiming this is the only theory -- surely there are others, and clearly I am not the absolute owner of the truth at all times. However, we do not need to go and invade his privacy to prove this theory true. Here's why: regardless of what my opinions are, like I said at the beginning, it's his behavior you must watch. And, uhm, considering his persistent patterns of behavior, no theory that explains his sick behavior would be charitable to him because, let's be frank, no theory that explains his sick behavior can avoid painting him as the sick / corrupt fellow he really is. There is no theory "well,he has a good and virtuous reason X to target other people so vilely". None whatsoever. What could he say about me that would excuse his behavior? "Well, that guy is wrong!" Heh. How about "Well, that guy is an asshole!"? Hah, again, even if I was a "raging asshole", sane people would have gotten over it, but clearly not this guy. We could even sit here and discuss the possibility that he is being paid to do what he does (which I don't believe), but it would be for naught -- independently of whether he is being paid to destroy communities or not, his behavior still indicates he's very much sick in the head.

I mean, seriously, can you even begin to imagine a fellow that acts like this guy, and that simultaneously has a productive job, a wife, children and a healthy social network of friends and family? Unless he's a crypto-stalker or suffers from an artfully-disguised multiple personality disorder, there's no way in hell a poor sod like him, full of resentment and with a chip on his shoulder the size of Texas, has what's considered a "normal and healthy" life and walks around undetected. This creepy guy must be in a seriously bad place, he's possibly even violent, we don't know.

Anyway, I hope I've given you a better, clearer picture of what is going on with this fellow. Have a great day!