Antitheatricality is the idea that theater (plays and performances) is bad and can corrupt people's morals. It's like when your parents say that you can't watch certain TV shows or movies because they are not good for you. Some people thought that watching a play was like that - it could make you do bad things or think bad thoughts.
A long time ago, some people believed that plays were dangerous because they could make people forget about important things, like God and the Church. They thought that plays were sinful and could lead people astray. In fact, some people even tried to ban plays and stop people from going to the theater.
But luckily, not everyone felt that way! Some people loved going to the theater and watching plays. They thought that plays were a great way to learn about the world and to understand other people's lives. They believed that plays could help people think about important issues and problems in a safe way.
So, antitheatricality is the idea that theater is bad, but not everyone thinks that way. Some people love going to the theater and watching plays, and believe that plays can help us learn and grow.