Nobody wants to face ugly truths. And even fewer want to confront them on television. That’s what makes the documentary “Worse Than War” (8 p.m., PBS, check local listings) so difficult and compelling at the same time.

Author and professor Daniel Jonah Goldhagen has spent his professional life studying genocide. His 1997 book “Hitler’s Willing Executioners” challenged prevailing ideas about the Holocaust. With “Worse Than War,” he looks at genocides of the past century in countries across the globe and finds common threads and disturbing similarities.

He’s not afraid to pose brutally frank questions. He interviews an imprisoned perpetrator of the Rwandan massacres. What was it like to use a machete on your neighbors? The killer relives the past at length and at times thoughtfully, saying that he often felt as if he were in a “fog” and at the same time feeling as if he were invincible and had conquered death itself. He also explains how he was recruited and manipulated by the political leaders behind the Rwandan genocide. It’s a harrowing interview — a conversation with an ordinary man and a glance, perhaps, into the face of evil.

Goldhagen frequently reminds us how mere words are not enough to describe genocide and how we often use language to deceive ourselves about the nature of the crime. We call such acts “unthinkable,” yet there is ample evidence that killings from Guatemala to Germany, Armenia, Rwanda, Darfur and Cambodia were carefully planned, organized and executed.

We call such acts a crime against “humanity,” yet time and again human impulses such as resentment and fear are essential elements of genocide. People think of such nightmares as acts of mass hysteria, yet Goldhagen shows how each mass killing spree was inspired by deliberate leaders who saw genocide as a means to a political end.

By the author’s estimate, more than 100 million people have been victims of genocide in the past century — more than the total battlefield deaths in all of the wars during the same period. This gruesome fact makes the title, “Worse Than War,” doubly true.

• “Human Target” (7 p.m., Fox) wraps up its first truncated season with a glance back at how Chance recruited his team.

• “Ugly Betty” (9 p.m., ABC) signs off for good. This once-promising show was not helped by frequent schedule shifts. And somewhere along the way it lost its heart, concentrating on brittle characters and hard-to-believe plot twists.

Tonight’s other highlights

• Katie Couric hosts a prime-time “Sesame Street” special “When Families Grieve” (7 p.m., PBS, check local listings).

• The documentary “Making the Crooked Straight” (7 p.m., HBO2) profiles an American doctor in Ethiopia.

• Two go home tonight on “American Idol” (8 p.m., Fox).

• A coaching vacancy sparks a rivalry on “Modern Family” (8 p.m., ABC).

• Death row can be murder on “CSI: NY” (9 p.m., CBS).

• “True Hollywood Stories” (9 p.m., E!) profiles Tiger Woods.

• The 2002 documentary “Standing in the Shadow of Motown” (9 p.m., TCM) celebrates the unknown studio musicians who created the record label’s signature sound.