Right, that's true if you're connecting them randomly -- you have a 50% probability of getting it right either way.

But if your intent is to connect red to positive, and black to negative, and you do that fairly reliably but with some chance of a mistake, then there are twice as many chances to make an error, and your chance of getting it wrong by making an odd number of errors is higher (although not exactly twice as high, which I incorrectly implied).