I think the crucial difference is being related to the people you are critisizing.
Anyone can critisize capitalism, atheism, the Church, Hollywood. That is their right. Usually they would like their criticism to a bigger argument about what it is to be a human being; how can society be better, going forward. These types of opinion polemics are designed to promote debate.
Sometimes people in the know critisize an industry, e.g. former teenage models critisize the modelling industry and the importance placed by it on being very thin. Former child footballers critisize the ruthlessness of the Club system. If they do this, they are seriously arguing for radical reform or abolition of these industries.
Meghan and Harry claim to be presenting their personal story. Their argument, purportedly, is that they received unequal treatment. They would like their children to be Prince and Princess and they are using and wishing to retain their titles into the future. They are neither presenting an argument against privilege or against monarchy. It is useful to them on the terms they want to set.
They have slurred the Royal Family in the process of making their case to have been unfairly made unpopular by the press and specific royals of a similar generation, i.e. William and Kate, but not Prince Philip who made hugely inappropriate comments about racial characteristics, but apparently is ok, cos he is like a vote royal and not in competition with them for popularity.. But if the public rallied and wrote petitions to have Harry do more royal duties in his manner of doing it, the couple would be pleased. They are invoking all sorts of arguments to try to make themselves popular again, but they haven't got a serious purpose in mind - just using the royal family in whatever way seems most useful to them at any one time.
This may change, and they might in future say they believe that the British Monarchy ought to be abolished. This would be fair, if they believe it, and it seems to be the logical end game of their mission.
However, in the absence of any points to support that anti-monarchy interpretation - e.g. a public statement when they accepted the JFK Foundation Award, rather than a soft peddle,counsellor speak about stating out own truth, it looks like a personal profile improving campaign and it looks too like subtle blackmail. It is a drip, drip of damaging statements and some weird veiled threats, like in that article on which Meghan looked fearsome in green, like you'd visualise a beautiful witch from The Lion the Witch and the Wardrobe or the Queen from Sleeping Beauty. She was saying that she hadn't signed anything saying that she would not speak out and she can be silent or vocal as she chooses. She was doing threatening in an artistic way.
So the couple don't have the honesty to say what they do mean. Or rather they have no serious meaning, they just want greater popularity, more money and a high profile. The royals are just their stepping stone to get it.
Harry has thrown his family under the bus. He will say anything to suit the moment. It has started to damage the serious role of monarchy, well the JFK Foundation award did, the only thing, I'd say. But he doesn't stop for breath.