I don't know what your reasons against are, but a big one for me is an infringement on one's right to assemble. I know it doesn't sound like much, but for a lot of communities (especially ones that may already be "targets" for law enforcement at all levels [local, state, and federal]), surveillance may keep them from feeling safe protesting.

For example, imagine being undocumented and wanting to protest. You may second guess going to a protest (even if it benefits you to do so), because you learned law enforcement is tracking the communications and movements of protesters.