When I read those types of e-mails, I can't help but ask myself - what was the writer hoping to accomplish by writing that e-mail? And that's the exact question you should be asking yourself before writing that kind of e-mail to your supervisor. Without knowing much about who you are and where you work, I assure you that sending an e-mail full of criticisms to your employer is not going to (1) make him treat you better or (2) get you promoted. At best, it will cause some type of personal friction between the two of you, and at worst - it will encourage that supervisor engage in a campaign of retaliating against you, micromanaging you, writing you up and even trying to fire you. Whether it will be legal or not is a different story, and that will depend on what you complained about and other facts. But, the bottom line will remain the same - your supervisor will try to make your life harder regardless of what the law says about his actions.
So, before you consider writing that harsh e-mail, consider (a) whether it's really worth sending and what the goal of that e-mail is; and (2) have someone else more "objective" review your e-mail before sending it out to make sure it doesn't appear more harsh than you really want it to be. Usually, unless you are ready to quit, giving your piece of mind to your manager has way more risks than benefits.