The ECHR is embedded in many laws and policies for example through the HRA public authorities such as Government departments, local councils, police, schools, certain care providers, and prisons, must act in a way that is compatible with the Convention rights.
The Good Friday Agreement would have to be reviewed which could cause violence and other agreements would need to be reworked.
The ECHR is described as a 'living instrument' which means that it develops according to social norms, meaning that human rights protections continue to evolve.
I've already described how governments could potentially take away human rights and how the government won't be able to be challenged.
Additionally, it's a way of making changes through the back door. Essentially what ministers are telling you they want to do, isn't feasible. The rights of asylum seekers are already covered under instruments such as the Refugee Convention.
The Supreme Court judged the Rwanda scheme unlawful under the principle of non refoulement amongst other laws, which are already covered under different Conventions.
Like Brexit, you're being sold a lemon.