However, there is clear evidence that even well-intentioned, professional people tend to be affected by their affiliations. They tend to have biases toward arguing or acting in favour of the interests of their affiliations. This can happen subconsciously, even against the logical desires of the person. It's well documented in other fields, medical research particularly, and there are various psychological experiments you can do to demonstrate what is thought to be the underlying behaviour involved.
No matter how logical and dispassionate we try to be, our wetware just appears naturally to have a predilection for biasing us towards groups we are members of. There is no good reason to think software people would be immune to this.
Rather than deny this general fact, the best thing to do is to acknowledge it, so we then can find ways to minimise it or work-around it.