Why are people on the internet so rude and stuborn?

Not all people on the internet are rude and stubborn. Some are genuinely helpful as well. Some people may be rude because the internet offers the shield of anonymity (no one will ever know who they are in real life), and generally there are little to no repercussions for a rude Word said online, where as in real life depending on the situation you could get fired or get into some sort of physical altercation. Their normal restraints when communicating with their fellow man/woman may or may not be in place due to this shield.