Now there's the obvious reason that more surveillance can catch more criminals, achieve more justice, deter further crime, and thus lead to a safer society. To those who suggest that citizens' privacy will be violated in our quest for more safety, I say this: our privacy will be destroyed anyway. According to historical trends, coupled with the current political climate, the government will only continue to add more cameras, initiate more surveillance programs, and expand. Thus the only recourse to check the power of an overreaching government is to add more cameras that are able to document the every action: actions undertaken by the public and by the government. Thus it is meaningless to debate national security with the assumption that we still have privacy, because that assumption isn't based in reality.
Finally this third reason may be a bit... strange. Individuals are selfish creatures who often act within their own self-interest to achieve a goal, even if that means harming others along the way. There are countless examples of corporations, small groups, and individuals harming others to achieve a personal or professional goal. Thus it's far better for the government, which generally consists of a more educated subsection of the populace, to make decisions on behalf of the public even if the public has no say in the decision, or the government obtains their data through privacy-violating means. Thus, it is for the above reasons that I am pro-surveillance.