Nothing is so enticing as watching someone making an obvious mistake over and over again. The temptation to take over is just about overwhelming.
On my phone I've seen ads for puzzle games where the ad shows someone attempting, and failing, to solve puzzles that look simple. I'll bet the ads are effective-- I find myself aching to show them how it's done. I'm not going to download their game, but I'd be willing to bet a lot of people do, just to solve it "the right way" and end the frustration of watching someone fail over and over.
I've experienced the same effect in real life. If I see a person fumbling with (what I believe is) a simple task, it takes all my willpower to not intervene and do it for them. Maybe they'd even appreciate my help. But until or unless they ask, as long as it's not a life-and-death situation, I've realized it's probably not my place. No one learns if someone else always does it for them-- so you're not really doing them a favor in the long run.
The same goes for people making really bad arguments online. Maybe that's really the best they can do with what they believe to be true. Or, maybe they are just trying to bait you into an argument-- sometimes you have to assume they can't actually believe what they are saying. Stop and think before diving in. If you want to come to someone's defense-- and it seems they'd appreciate your help-- go ahead. You're not going to convince the person making the bad argument, though. If that's your motivation you'd be better off scrolling past.
Don't become a victim of your own helpful instincts by "helping" where you're not really helping.
