This is such a weird take. Minecraft was never made to be a children's game. It was always an "all ages" thing. To this day, the game is not juvenile - it's made for anyone to be able to enjoy. That it is popular with kids has always been a happy accident resulting from it enabling creativity and more importantly being extremely easy to learn. So yes, "grown adults" who form the core playerbase absolutely get to have an opinion on the franchise they've supported for 13+ years.