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.