system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What does the NSA do exactly and why is it so bad?

I always hear about the NSA but I honestly have little knowledge about the group and what they do.
gpt
It's signals intelligence - i.e. they are concerned with the content of communications between parties of interest - which traditionally means other intelligence agencies, foreign governments, enemy combatants etc. When you get mission creep into routinely snooping on the private communications of ordinary citizens without any particular justification, that's when people don't like it.