The Character Plague of Times Square!
Bird's Eye View of Times Square, New York
The primary argument against VT is that there is no correlation between the ad- vertisment that ran and the action that took place. Even if the pixel fired and the user was cookied, a different ad that generated a click was responsible for that conversion. in short, a lack of clear measurement drives the lack of a clear answer.
I actually think it goes further than that, and includes questionable tactics in use by media owners who are trying to inflate their real value, and given that occurs, I sympathize with the marketer who is being encouraged to give credit for it.