Okay, imagine you are at a park, and like many parks, they have different playgrounds. One playground has a big slide, monkey bars, and swings that are pretty high. Another one has a smaller slide and a sandbox with toys. Now, imagine that some kids think that only the big playground is cool, and they make fun of the kids who like the smaller one. They say things like "you're not a real kid if you don't like the big playground" or "the smaller one is for babies." This is like rockism.
On the other hand, imagine that some kids think that both playgrounds are awesome and that everyone should enjoy them both. They say things like "I love the slide on the big playground, but I also love the sandbox on the smaller one" or "everyone should be able to play where they want and have fun." This is like poptimism.
In the music world, rockism is the idea that only certain types of music, like classic rock or punk, are cool or legitimate. People who believe in rockism might make fun of other types of music, like pop or hip-hop, and say that they are not "real" music or that people who listen to them are not "real" music fans. This is like the kids who make fun of the smaller playground.
Poptimism, on the other hand, is the idea that all types of music are valid and worth enjoying. People who believe in poptimism might love pop music and also rock music or hip-hop or any other genre. They might argue that music is about having fun and enjoying yourself, not about fitting into a certain category or being "cool." This is like the kids who think both playgrounds are awesome.
So, in short, rockism is when people think only certain types of music are cool or legitimate, and poptimism is when people believe that all types of music are worth enjoying. And just like in the park, it's okay to like both or any type of music you want!