It reminds me of what were called "Fifth Amendment Communists" during the fifties, a time when Communists had systematically penetrated the US government and the House and Senate held investigations. (If you're some kind of pinko, you may prefer to think of this as the McCarthy Era, or the Red Scare. ) As pro-Communist writer Ellen Schrecker put it, "Though a legal godsend for uncooperative witnesses, the Fifth Amendment became a public relations disaster. "
The reason Communists who may not have been spies themselves didn't want to testify at all is because they didn't want to betray their friends who were. Muslim terror sympathizers will be doing this for the same reason.