I do think we should be open to the opinions of others, especially those that are different to ours, so we can learn and develop our ideas. However just like we would look for a credible reference if we were going to write an assignment, we need to consider the source of information. The problem is that we feel GPs should know about these things but really, why would they? They are specialists in disease diagnosis, not child development/psychology.
If you are up to it, you can argue the point but make sure you are well armed with evidence and a tough skin. The benefit to that is that you may just change their mind on a subject or at least get them to think enough to look into it for themselves.
Sometimes it is just better to nod, smile and leave being comfortable with your own decisions.
HTH