A successful resaurant is looking to replace a failed one, great! Yes, I am familar with the problems of locating an In-N-Out in too small a location, look at the location in Mountain View on El Camino. Proposed site is much larger than even the Airport location.
I am not an expert on traffic flow, I have confidence in the people that are, City's Planning Department who will conduct a thorough review of the proposed restaurant, including analyzing potential traffic, parking, circulation, public safety, noise, lighting, odor, and air quality impacts. Let us wait for the study to be completed before rejecting it out of traffic fears.
In-N-Out pays their workers above minimum wage, and should be a welcome edition to Campbell.
As much as I would like to have an In-n-out closer to home, I have to agree with the traffic concern. If the rear parking could somehow be converted into a smarter queue for drive through that can take at least 20 cars, it might be ok. Keep in mind that an In-n-out building won't have as large a footprint as the elephant bar does. The way the drive through queue spills into the parking lot by the airport is totally dumb. If they can innovate and come up with a smarter layout for the drive through, I would patronize this location.