What is the main function of homeland security? ?

Homeland security's alleged purpose is to increase security and safety of the citizens of say Canada and the US from, in particular terrorist threats such as the 9/11 attack on the World Trade Center in New York. While it is understandable that this attack constitutes a strong reason to increase security for the American citizens and it was a heinous attack but it it is also well to remember that the best security is fighting for the rights of all and showing respect for the territorial integrity of other countries, helping them deal with natural disasters with relief aid, etc. In fact, homeland security is also used to repress citizens just because of their race or color such as islamophobia.