Here is Trey Gowdy, former prosecutor (never once lost a case) articulating to the media, the unanswered questions that justify the request for additional hearings.
These are significant questions. Have they been clearly answered already? If so, Gowdy whould explain why he says they are unanswered. If many of these are still unanswered (and I can't fathom why these wouldn't have been answered yet), that's valid reason for the hearings.
The Dems do not want thee hearings. Human Nature 101 suggests that when one has noting to hide, one does not quiver at the thought of answering a question.
The GOP picked the right guy. Sharp, committed conservative, won 100% of his cases as a prosecutor, and he's not a right-wing nut job, it won't be easy to paint him as a pure ideologue.