Without tools LLMs can do nothing more than emit text. You are probably assuming a harness is provided to the LLM with shell access but that is absolutely not necessary for LLM usage depending on the use case. For interesting stuff, you do want to provide some tools, but nothing with the power of a terminal if you are worried about security. A MCP server is perfect to securely provide the LLM with some controlled power exactly because it can do nothing at all other than call tools that go through the MCP server and can therefore be scrutinized, audited and ensure credentials are not visible to the LLM.