It's not immature to think periods are gross

Just because it's natural doesn't make it not gross. Everything that comes out of people is gross with the possible exception of tears. Urine, feces, blood, vomit, mucus, ear wax. All natural, all gross. Thinking periods are gross isn't wierd. There is no need to destigmatize periods. Bodily functions need to have a degree of stigma. People find a private place to deal with those things. It maintains civility.