Yes of course we can talk about people who choose to appear on tv, whether they're royal or not!
There's a difference between discussions and just plain making up shite to fit your narrative.
We don't live in the foreluck tugging 18th century any more!
OK 
Now if meghan and Harry were leading a private life, not sulignibg streaming deals, or giving interviews with Oprah, then absolutely I would support not discussing them and respecting their desire for privacy.
They do generally live a private life. Many celebrities do. That doesn't mean they can't ever be seen in public again, or earn money. They'll always be famous, doesn't mean they deserve abuse or be told to disappear forever because they won't play 'pretty prince and princess' anymore
.
But to suggest that they should be able to dictate peoples' response to their deliberately high profile, media-saturated lives is utterly ridiculous.
When the responses are abusive, made up based on hearsay and often racist, they are absolutely allowed to have a say on the matter. As anyone would be when hearing malicious rumours about themselves, which manifest whether they speak or not.