What is the main idea of this passage? [br] [originaltext]A libertarian think t

A libertarian think tank, reckon that eliminating all travel visas to the United States would add between $90 billion and $123 billion in annual tourist spending. By one estimate, introducing visa restrictions can lower trade and foreign direct investment between a pair of countries by as much as 25% .

Genes provide cells with the instructions for manufacturing proteins, among other things, and so inserting a functional gene into the body can, in theory, provide a lasting supply of whatever missing proteins a patient might need. But gene therapy has had a troubled history, in part because scientists cannot precisely control where a new gene inserts into a cell’s DNA and how active it is once there. These problems can lead to unwanted side effects — including the development of malignant tumors.