Many of the best TNG episodes feature the darkness creeping back in, with Picard acting as the guardian of the light they have worked so hard to create. The big example I have in mind is Drumhead. Picard recognizes fascism for what it is and immediately moves to counter it, delivering one of the best speeches of the franchise.

This wasn't a show that shied away from dark subject matter; there were multiple murder investigations, an entire two-parter about Picard being tortured at the hands of space nazis, two separate episodes about ordering crew members to their deaths...this show could handle weighty subjects, subjects weightier than "this character is being mean to that character." And it could do it with the fucking lights on.