I'm not normally one who likes to ascribe everything to a single cause, but with Karl I think you genuinely can say that every aspect of his character and history is explainable by one thing: autism.
Karl works (or worked) in tech. Because autism.
Karl collects a bunch of WWII krautoid militaria. Because autism.
Karl is an edgy atheist who joins the ultimate edgy atheist larp club, Laveyan Satanism. Because autism.
Karl feels the need to overcompensate for his suspicious fondness for kubelwagens, SS ponchos, and gas trap rifles by enthusiastically adopting and preaching far left politics so that his lefty techbro hAcKEr friends won't think he's an ebil noghtsee. Because autism.
Karl gets down bad for some extremely mid pussy and allows himself to be cucked out of fear of losing all access to the one female he somehow convinced to fuck him. Because autism.
Karl creates a splinter group of a splinter group of an obscure competitive shooting discipline with a focus on being hardcore and physically intensive (read: involving kettlebells) but immediately bends the rules as soon as they mildly inconvenience his fat retard friend. Because autism.
Karl pesters Ian with fanmail explaining that ackshually he should do his historical loadout tests at Karl's match instead of the rival 3-gun match because Karl's match is so much more rEaLiSTiC and 3-gun is fake and gay. Because autism.
Karl immediately tries to make the collaboration all about his special interests (nontraditional monetization models, cowboy larp, left wing politics, etc.) instead of what Ian actually wanted out of it (practical, objective testing of historical and modern weapons that wouldn't fit in with his normal short-form tabletop Forgotten Weapons content). Because autism.
Karl gets into spergy, tone-deaf arguments with fans in the comments and on social media, thus attracting trolls like shit attracts flies. Because autism.
Karl builds a weird gamer gun with a bunch of bizarre design choices and insists that ackshually this is the ideal AR body type and everyone else building ARs is a retard, and no it's not a gamer gun, MOM! Because autism.
Karl, influenced by his weird degenerate commie tranny hacker buddies, develops a raging case of terminal Trump Derangement Syndrome. Because autism.
Ian tolerates this for way longer than he should, and goes out of his way to appease/not upset Karl despite the fact that Karl's antics are damaging his brand and alienating his fanbase. Because Ian is also afflicted with autism, but the quiet, geeky, nonconfrontational type of autism as opposed to Karl's tone deaf neghole-pozzing tard rage autism.
Karl deliberately enters a thread on Arfcom where he is being mocked by boomers, has a giant spergout, gets b&, and then spergs out even harder, calls Arfcom a Nazi website and tells people to boycott it (despite the fact that Arfcom is owned by Brownells, the company that is selling his rifle project, and anyone with half a brain could probably figure out that actively shitting on your business partners and telling your audience to boycott them because a couple of boomers on a forum called you a faggot is a really stupid idea) resulting in his rifles being discontinued by the only retailer that was selling them. Because autism.
Karl fails to grasp basic social norms and aggressively lashes out at anyone who questions him, criticizes him, or tries to distance themselves from his increasingly unhinged behavior. Because autism.
When Ian finally puts his foot down and starts to quietly distance himself from InRange and Karl because TDS, leftism, tranny cocksucking, and insulting and mocking the overwhelming majority of gun owners is, shockingly, deeply unpopular with his audience and is putting Ian's reputation and business at risk, Karl treats this as a vicious personal betrayal rather than the very reasonable and polite business move that it actually was, and proceeds to immediately immolate that bridge. Because autism.
Karl tries to throw his weight around and dictate to Varusteleka who they are and aren't allowed to invite to their event, thus burning yet another bridge. Because autism.
Karl gets pissy and tells his (rapidly shrinking) audience to go after venues like the Pima Pistol Club that he depends on to host his events because he doesn't like some boomer ass memes that they post. Because autism.
Karl makes stupid public statements to Wired journos which draw massive negative attention to his matches, thus causing even the fat furry retard to say "fuck this guy I can't deal with his shit anymore" and further alienating venues that his entire grift is absolutely dependant on. Because autism.