wtf is the difference when 1) you put a key in front of the mcp 2) you mcp a whole bunch of privileged access.

it's like saying "i don't want to give Claude access to my file system but i'm fine letting it run bash" ......

The difference is that the LLM never sees your keys/secrets. My understanding is that can make a big difference.

Does mcp guarantee that, per se?

Not if you assume the straw man like grandparent, but yes if you use it thoughtfully.