He's arrogant and rude about it, which is bad enough when someone is right and worse when they're wrong and trying to teach beginners. In particular he doesn't understand object oriented programming (look at the piece he wrote about .each vs for in ruby), but is too arrogant to realise that there's something he's missing, so he goes on these sweary rants about how OOP is nonsense/useless/evil/what have you. In any programmer that would be bad. In someone who purports to teach beginners it's disastrous.