The exception means legally, that category of people, can't be prosecuted even if incriminating stuff were collected through such channels.

The next logical step, after a prosecutor or political push, would be for the Highest Order Courts of Member countries to invalidate evidence collected through such channels for those categories of people.

You are looking on it from a wrong perspective. You have access to communications of politicians, military and government apparatus. You can effectively control these figures through extortion (I know about your mistress) or blackmail (I picked up your kids from school today next time I may keep them for a while)

Politicians who are pushing these laws are having a feeling that bad things can't happen to them. However they are usually prime targets for bad things happening to them, because they are the ones wielding the power - if you can influence the politician, you can control his power.

Nope, not in Sweden. Anything can be used as evidence here, even illegally obtained stuff.