they have openly said that people who use encryption are of interest to them, or at least their communications are. however this is easily solved if there is wide enough adoption. If I encrypt the shopping list that I send to my other half, or I encrypt the text messages i send siblings or any text communication to anyone, and there are 100's of 1000's who do the same it becomes impossible to store/monitor and decrypt all that information. it would essentially overwhelm them with data, which even if they managed to decrypt (through the theft of private keys or a serious brute force attack) would be of no value other than to prove the task a waste of time.