First, coffee tastes like mud so the whole point is moot. If you serve flavored coffees, milk in coffee, soy in coffee, then there is obviously no integrity involved, just snobbery. Supposedly the best coffee bean in the world is collected from the droppings of a palm civet in the Philippines. No thank you. If you allow cream and sugar, why not ice? As for some pissant coffee jockey dictating what he will and will not serve, that is another whole issue.

No. That's ridiculous, the customer should be able to decide what they want.

This is like an architect only designing houses that he/she likes and not following customer's requests out of principle. Which is fine, they are entitled to do so - but the customer is also entitled to go somewhere else.