Defunding them would be as dangerous as defunding your military.
Maybe (probably) there is room to reduce intelligence budgets, but how and where is not so simple. Unfortunately it's a complex problem that would need study before anything is changed. These populist "defund" ideas sound good but are not the way to go imo
https://irp.fas.org/offdocs/int006.html
Here's page about "OFFICE OF CIVIL LIBERTIES, PRIVACY AND TRANSPARENCY - WHO WE ARE" https://www.dni.gov/index.php/who-we- are/organizations/clpt/clpt-who-we-are
It's so big part of it has the job of keeping the rest of the organization in check.