What about the vacuum part?
The correct phrase is "speed of light in a vacuum". But there is no perfect vacuum. Space is full of plasma. Even the least dense areas of space are not a perfect vacuum. So is it possible that a photon could travel 14 or so BILLION years and not encounter some form of plasma ion? And even if it doesn't collide head on with an ion, wouldn't the charges involved modify the trajectory, however minuscule that modification might be? And wouldn't multiple interactions invoke multiple modifications?
And then there's all those neutrinos. We are told billions of them are passing though out bodies every second. We are also told they "rarely" interact with matter, but "rarely" is not "never".