Privacy

For the most part the terror is theoretical. As others have mentioned there is no practical difference between surveillance companies and three letter agencies, there is a revolving door of employees and information between the two and almost no sunlight between them. Having said that the dystopian fears of misuse are well founded, but as of yet mass surveillance has only really been publicly misused on the personal level. Cops and agents using flock to stalk people, local law enforcement using them in oppressive ways, but we haven't yet seen it applied at scale.

Realistically, those tools allow for heavy handed control, but Americans are still Americans, they need to be coaxed into being okay with large groups being rounded up for exercising their right to free speech. That's really where the true danger lies. The Algorithm heavily shapes the opinions of the masses and it is currently and actively being used to do just that. I could write extensively about the how's, why's, and who's but that's way beyond the scope of your question. Suffice it to say the feed controls the shape of the debate so that there are only two sides when in reality there are dozens for each issue. Just ask yourself when was the last time you saw a post suggesting cutting military spending or getting rid of gendered sports in favor of weight and height based groupings?