Why are some online gamers ignorant, obnoxious, and defensive?

Why are some online gamers ignorant, obnoxious, and defensive? - 1
Added (1). I was on my Steam account having fun playing Team Fortress 2 which is a free multiplayer game btw and I was playing Man vs Machine as an engineer. Well to be fair? I'm not very knowledgeable in games when it comes to the role of certain classes in a game like TF2, but apparently these two other players didn't like the way I played and pinned the responsibility of me and the other engineer losing, so I decided to speak up and tell them chill out, but they continuously try to insult me.

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