SONOMA, Calif. — This kind of list makes David Letterman sick to his stomach and question his love of auto racing. The retired late-night comedian and IndyCar team co-owner rattled off a number racing deaths — Justin Wilson, Dan Wheldon, Paul Dana, Dale Earnhardt, Ayrton Senna, sprint car driver Kevin Ward Jr. — and wondered if "maybe we've reached diminishing returns at making this sport safer." Letterman expressed his grief in a telephone interview with the Associated Press from his Montana ranch. He spoke two days after Wilson died from a head injury suffered Sunday when he was hit by a piece of debris at Pocono Raceway in Long Pond, Pa."It's just like, 'Whoa, is this really the sport that you can embrace entirely?' I don't know. It's a real self-examination," Letterman, 68, said. Letterman is part-owner of the Rahal Letterman Lanigan Racing, and the team goes into Sunday's season finale at Sonoma Raceway thick in the championship hunt. Graham Rahal trails leader Juan Montoya by 34 points in an event that will count for double points in the standings. Rahal was just nine points out headed into last weekend's race at Pocono, but he was wrecked by Tristan Vautier midway through the race. The incident with Wilson occurred long after Rahal had exited the race, when debris from Sage Karam's single-car spin flew into Wilson's open cockpit and struck him in the head. In a coma and critical condition, the 27-year-old died a little more than 24 hours later. He leaves behind a wife and two young daughters. "I talked to a lot of people about this: Racing is fun, but people are not supposed to get killed," Letterman said. "I am brokenhearted for his family, for his kids, and everybody says, 'Well, this is what the guy wanted to do.' And of course, that's the case. "But we're not supposed to have people die in the middle of this competition. I think he has two children, and that just breaks my heart, that dad loves driving race cars." Letterman's voice was emotional and it was clear he has put much thought into justifying his love of racing against his personal struggles with the risks involved. Improvements were made after the death of Wheldon, a St. Petersburg resident, in the 2011 season finale in Las Vegas. The two-time Indianapolis 500 champion died almost instantly when his car went airborne and his head slammed into a post in the fence. The car driven now in IndyCar was introduced immediately after Wheldon's death. Dallara, the open-wheel car manufacturer, called it the DW12 for the development work Wheldon had provided. Wilson's death was the first fatality in IndyCar since then, and it was almost a fluke accident in that the nose cone from Karam's car bounced down the track and into Wilson's cockpit as he was the 12th driver to pass through the crash scene. "I've done quite a lot of thought, and statistically, I suppose people will tell us racing has never been safer, and maybe that's the case," Letterman said. "And it seems like always enough time goes by between episodes, tragedies like this, where you are lulled into thinking that, 'Okay, well, that's not going to happen again.' "And then it happens again. It just makes you sick to your stomach." IndyCar is honoring Wilson this weekend. It began Thursday when Marco Andretti drove Wilson's car across the Golden Gate Bridge. James Hinchcliffe, who has been sidelined since his own life-threatening accident in May during preparations for the Indianapolis 500, was scheduled to drive IndyCar's two-seater with the championship trophy in the car. Letterman remains excited for Rahal's prospects on Sunday, but his emotions are tempered by the loss of another driver. He said he struggled this week reconciling the good and the bad of auto racing. "What other sport do you have these two diametric circumstances: One, the possibility of this kid winning his first championship, and then also in the same week you have a guy who dies. I don't know how to reconcile it, I just don't," he said. "When you see a race and you see people drive these cars with such precision, what they are able to achieve and what they are able to control, it's like watching ballet. What they are able to do with these high-horsepower automobiles, it's like watching the Blue Angels or something," Letterman said. "That's the thrill of it. So when you see a kid get killed doing this, it's a tap on the shoulder of, 'I don't know. I don't know if we are supposed to be enjoying this or not.' Not many people are getting killed in volleyball."