The reason #ownvoices became a thing wasn't about gatekeeping. It seems that way from the outside until you actually look into the statistics and lived experiences that make it necessary. It has to do with making sure that stories about marginalized people are authentic and not harmful, and it's also about highlighting and fighting the opportunity and pay discrepancies in publishing.
Authors of color, especially Black and Native authors, make up a tiny percentage of those who get published, and they are often considered niche. "There's no market," publishers say, but they also spend very little money in marketing those authors, so it's a self-fulfilling prophecy. Protagonists of color are much rarer than white protagonists as well, and an author is actually more likely to get a book with a protagonist who is BIPOC published if they are white. The same goes for trans stories and trans authors; cis authors get the priority. The same goes for stories by disabled authors and about disabled experiences; abled authors get the priority. Same with narratives that explore immigrant experiences, impoverished experiences, gay experiences, etc., etc. And white, cis, hetero, etc., authors are also routinely paid a lot more than those who are more marginalized. All of that, I hope we can agree is deeply unfair and, to be real blunt, ass backward.
Most of the time, authors don't get rejected for writing about marginalized communities of which they are not a part, even when their stories are deeply misguided or outright harmful. Rejections do happen, as was mentioned, but that's rare. #ownvoices is a good thing (when it isn't misused). It's seeking to make publishing more equal, not gatekeep.