Well, we do know that two doses of the MMR provide 97% protection against measles, one dose around 93%.
Since you seem keen on facts, this is from the National Foundation for Infectious Diseases
Even in a mild case, measles is a miserable disease with high fever, sensitivity to light (photophobia), dehydration, cough, pneumonia (1 in 20), and rash. Measles can result in seizures, deafness, blindness, permanent lung damage, and immune amnesia (wiping out of prior immune protection). Measles can weaken the immune system and the central nervous system, leading to serious disease and even death years after measles infection. Estimates show that 1-3 out of 1,000 children with measles will die.
I'll take the 97% odds of none of the above for my DCs. Since I'm not a moron.