Well, more precisely, reddit (and the internet in general) is obsessed with informal fallacies. I've rarely, if ever, seen someone point out a formal fallacy. I assume this is because formal fallacies are more bookish and difficult to identify. One formal fallacy I've become rather decent at identifying is equivocation, or "the misleading use of a term with more than one meaning or sense (by glossing over which meaning is intended at a particular time)". However, to my chagrin, I've noticed that the use of this fallacy is often taken as cleverness, and the person who uses is generally greeted with lots of upvotes by people who, in all honesty, don't care one way or the other about the argument and merely support whoever says stuff they believe in.
I've noticed something funny about the way people generally use the term "logic" or "reason". Do they mean that they break their arguments down into Aristotelian terms, or some other formal logical system, and analyze the truth values of each? No, generally, they do not. Generally they mean something like "intuition", and are simply putting on airs. I would love to see the person who uses logic and reason and decides that, after all, his views are wrong. Instead, we see millions throughout history saying "I have discovered objective truth, and wouldn't you know it, it just happens to be everything I believed in"! Of course, I am going to draw fire for this statements. However, it is one thing to say there is objective truth, it's another to say you know what it is.
With informal fallacies, it is unfortunately true that a lot of them are, well, common sense. Think of, for instance, correlation equals causation. Of course if something happens once, it's more likely to happen again. That is essentially the basis of science, it is otherwise known as "induction". I suppose that, on some level, there's always the possibility that inductive reasoning could've been flawed. But it becomes massively unlikely after a while. An experiment is much more likely to be wrong because of error than random factors inexplicably overwhelming the results. It's really not even worth considering. Humanity is engaged in a struggle for the truth, there's nothing wrong with probabilistic evidence, as the signal will typically emerge from the noise in the long run.
However, in typical experience, I've become somewhat cynical about the usefulness of arguing. The arguments that people use often aren't even particularly important in themselves, they're just facades people throw up to shield a belief. When someone loses an argument, they usually just switch to another one. This is what Nietschze was getting at when he famously used the tactic of looking past the argument itself and merely considering what type of person would make such an argument - examining their inner motivations. Which is actually somewhat sensible, since the argument itself is so rarely the important subject. However, if you think about it, that's an ad hominem attack, is it not?