These was bound to happen eventually as the technology culture evolves. The master/slave terms was more then likely not the best terminology in the start and does not help those who are not technical understand what it is up front without thinking about slavery at first.
If you know someone who was a slave, had it as apart of your family history or are currently living in illegal slavery the master/slave naming can be very offensive and in some cases trigger PTSD from events that occurred to you in the past.
With the changing to something easier to understand and more neutral it removes the bad baggage that comes with the initial terms and in most cases helps people new to the technology understand or at least relate better to what is going on.
I've had colleagues pull me aside for advice on better terms to use than the defaults so they would not offend their coworkers, current and potential customers or other friends. If you feel embarrassed or wrong about the master/slave reference there is a good chance it will cause some issues spoken and unspoken as there are better alternatives for it that are more in line with our modern cultures.
Changing master/slave to primary/replicas is more appropriate as it helps people understand what it is at first, has no bad baggage associated with it and easier for non technical people to understand.