Politically? Physically? Culturally? Morally? Currently Hong Kong is ruled by China. Many in Hong Kong might prefer something different. If the government in Beijing allowed them to, they might choose complete independence.
> why should GB be able to dictate Chinese law based on a colony they took from China hundreds of years ago?
Why should a government in Beijing be allowed to dictate policy for people in Hong Kong based on the fact that Hong Kong was under control of a different government in mainland China hundreds of years ago before the British (unlawfully) took it from them?
Should the people of Hong Kong have a say in this? The people in Hong Kong have been asking for the right of self-determination. Is there some reason that the people of Hong Kong should not get this right?