Have you ever performed, blood test and necropsies on your birds to confirm your findings that it was not causing any damage?
As you anecdotal evidence isn't supported by empirical/scientific evidence and studies...
I have read it state more times then I care to count on just this forum, as well as by many other sources...
Again many people on this forum avoid layer feed for mixed flocks with roosters and/or other birds, it's quite common...
As for a 'mentor' that is would be a and
ad verecundiam fallacy, and doesn't dismiss the scientific data that might contradict their opinions just based on their proclaimed authority...
There are multiple scientific studies showing the damage to the kidneys that excess calcium can have in non-laying poultry...
Just Google it up...
http://www.thepoultrysite.com/articles/2337/urolithiasis-in-male-broiler-breeders/
http://ps.oxfordjournals.org/content/87/7/1353.full
http://www.ncbi.nlm.nih.gov/pubmed/7335125
The Merck Vet Manual even considers excess calcium to be a poison...
http://www.merckvetmanual.com/mvm/poultry/poisonings/overview_of_poisonings_in_poultry.html