It's always drilled into us that we shouldn't use comma splices. They're bad, to be avoided and poor form.
But why? What makes the comma a faulty choice in something like this:
I never liked school, it was boring and repetitive most of the time.
It could be replaced with a semicolon, dash, period or colon and be "correct." Yet to a fair amount of people, the comma seems fine. If it weren't, it wouldn't be found so often in online forums, text messages, emails and so on.
What makes the comma between two sentences an error?
