It basically boils down to this, Kat. A lot of people (well, most people...) simply love to here themselves talk. It confirms and strengthens their own sense of their identity.

So, no matter what is ever being discussed here, a variety of people will drop in and do that...and their opinions will always vary. A person whose opinion diverges widely from the majority will generally feel that they are considerably smarter than the majority, and they will enjoy fighting over their differing opinion with the majority. The majority, on the other hand, will generally feel much superior to the lone outsider (or two) and they will enjoy ganging up on those outsiders and thoroughly castigating them...hopefully driving them finally off the thread. The more the these two sets of people fight, the nastier it gets, the more stubborn they all get, and the greater becomes their emotional investment in defending their chosen position (whatever the heck it is), and the lower sinks their respect and courtesy toward those they are contending with.

And there you have the Internet! ;-) It's a battle of flaming egos, conducted at a safe distance, with a singular lack of regard for the kind of restraint we might all normally show when dealing with others face to face.

On the other hand, to look on the positive side, it can be quite mentally stimulating and entertaining at times if you don't let the rancour get you down too much. ;-D