Lobbying must be allowed to exist. You bringing issues to the attention of your representative or asking them to change some policy is lobbying. It is even very useful to allow organizations to lobby politicians. For example, I want EFF to be able to lobby politicians about things I don't have the time or influence to really push for political change on. I do wonder how we could effectively restrict corporate lobbying in that context. Maybe there could be a special type of charitable nonprofit that is more restricted, such as only being allowed to accept funding from individuals rather than corporations and then deny lobbying rights to anyone acting as agent of any organization other than one of that sort? But I think we're very far from a political environment in the US in which any constitutional amendment restricting personal rights in the political process would end well.