Why isn't the paperizzi stalking people, and invading their privacy at their homes to take photos illegal?

there are some celebrities like kanye west, cash warren, and heath ledger who have gone after people filming them and taking photos- like hit them, etc. some stars like halle berry and even brad pitt have sued people for trust ping on their own property. like shouldn't this be illegal, some of them trust p on people's property, make stories to defame people's names, etc. even princess diana died trying to get out of the lime light. it makes me wonder, how can someone just get in your face with a camera, follow you for 10 blocks, and not be arrested.