I don't think comparing the modern day monarchy to slavery is a sensible comparison
Why not? Slavery was something that this country had. We got rid of it - but I bet there were lots of people complaining.
Same for other radical changes. Eventually people realised that the system was outdated.
Eventually, people will realise that about the Monarchy. They will be a historic, irrelevant relic. In many years time, children at school will wonder with amazement that the Head of State was not picked by a vote but because of birthright. They will be stunned that the anthem asked God to save the Queen. They will be amazed that we had a State religion. That the media fawned over these people.
I don't know how many years in the future that will be - but it will happen. The Royal Family are subject to more and more media observation now and can easily fuck things up. More scrutiny. It nearly happened after Diana died.
Future generations will be amazed at how such a family came to be the one family out of 60 million people who had such power.