Why don't 'real' BC people like Merle BCs?
Not to go too OT but...
My understanding is that it's partially because sport-bred dogs have a much higher % of merle, as a group, so when they see merle they think sport-bred. And for-sport breeding is reprehensible and undermining BCs as a working-only dog and the dogs produced aren't actually BCs, by their way of thinking.
Another reason, is that since merle X merle is a dangerous combination they consider merle a gene that is there just for aesthetics, contributes no benefit to the dog, and is potentially harmful to the dog. Therefore if it happens it happens but it should not be sought out nor bred unless the dog is exceptional, and then never to another merle of course.
Not saying the above does or does not reflect my own views since I don't want to derail further...just trying to answer the question itself.