Banned for life over one email

A 17-year old British teenager has been banned from entering the US for life after he sent an email to White House, calling President Obama a "pr*ck". Hurray to the FBI for acting tough; but isn't that using a sledgehammer to kill an ant? How is it that terrorists and their sympathizers can chant death threats against the US openly and get away with it, while a derogatory remark, which is not even a threat, is immediately silenced and crushed? If the FBI were to ban every person who openly shouts threats to the country, I think it will save them much time and money having to deal with it later on.