YouTube sure as hell can't silence you, other than by refusing to host your content on its servers, and federal, state, and local governments can exercise similar control over content hosted on government servers.
Congress has much more freedom/power to pass laws limiting the operation of the Executive than it has over private activities.
This is part of the reason all sorts of government surveillance is structured as private companies that curate data with the goal of providing it to the Government. Companies are much more free to generate whatever databases they like, however they want. Government use then falls under the vague category of accessing "business records" which Congress ultimately doesn't seem to regulate much (except perhaps for medical records and wiretapping).
