But how many are killed because people are texting while their vehicle is stationary?
If you're texting while stopped, you're not paying attention to what's going on around you. Around my university, I see plenty of instances where kids are still in the crosswalk when the light has switched - or even will dash across as the light goes red because they think they can make it (and apparently assume they are invulnerable). If you're paying attention, you'll notice them. If you're texting, odds are you're at most keeping a partial eye on whether the light has changed.
Sure the kids are stupid when they behave like that... but if you hit them, you're also at fault for not paying attention. You're operating a large, dangerous piece of equipment. The social contract requires you to not just be thinking about yourself, but to be taking reasonable care not to hurt or endanger others.