Being spied on by your own country is worse than being spied on by other countries. Your own country doesn't have another country between you and it to protect you. Also, other countries will look at the USA and say 'we can do it because they do it', and that just leads to more problems. Eventually you have to say no to spying. It's morally and ethically unacceptable, and we should not tolerate anybody doing it.
When a country wants to spy on it's own citizen, they apparently think that it's acceptable to ask for that data from another country as opposed to being illegal when getting the data directly. USA <-> Germany being an example