If you are looking for something to copy and paste in your messages to the committee, feel free to use the following:
Dear Congressman (or Congresswoman),
On February 16, you will be holding a hearing on the monitoring of social media by the Department of Homeland Security. The DHS has been performing domestic surveillance of American citizens with no probable cause.
Governments have a bad habit of finding crimes wherever they look for crimes, even if no crimes are actually being committed. The idea we citizens have nothing to fear from our government spying on us if we are not doing anything wrong is grossly misplaced. If that axiom were true, there would be no need for the Fourth Amendment.
Being content with the idea of our government looking in more and more places for crimes without evidence of criminal activity actually occuring is very much against the American principles of freedom and liberty.
I hope you will protect our freedoms and direct DHS to stop eavesdropping on us citizens.
Thank you very much.
Why? Why do you care they have the authority to do it and arrest you. That will be their reply to you.