One can find I think here[1] quite good analysis of Roman inferiority complex towards Celts and other milk-drinking people of the North. Simply speaking dreaded Roman legions consisted of very short men and they weren't able to look down at 'unusually' tall Celts and others.

The ability to enjoy dairy had some advantages too.

[1]: https://www.goodreads.com/book/show/8078106-the-ghosts-of-ca...