Can you use readied actions to avoid being hit?
This came up in our game today; after I thought about it, it seems incredibly exploitable. Here are some examples of how you could avoid being hit. As a tank, if you give up your turn to waste the enemy's turn, then that's not so bad a trade.
You ready an action to 5-foot step back when somebody approaches you. You have now just become immune to full attacks as in order to full attack you, somebody has to 5-foot step towards you. Assume they are standing 10 feet away from you. When they 5-foot to get in range, you simply 5-foot back and their turn is wasted.
You ready an action to 5-foot step back when somebody attacks you. RAW says your step goes before their attack and then they finish their action. They seemingly cannot cancel the action and pick a new one. In this case, somebody standing beside you declares an attack, you step away in response, and they lost their attack.
Is this allowed per the rules? It seems broken.