"Using [Tor]" actually is the subject of that sentence. "Who's looking" is not the subject even of the dependent clause in which it occurs; "depending on" is introducing an adverbial clause, in which "who" is the subject, "is" is the verb, and "looking" is the predicate.
> Passive voice also elides these serious issues by pinning results on nebulous activity.
The passive voice is not used in the sentence quoted.
I recommend preferring rhetorical techniques other than grammatical analysis; even for someone with a solid understanding of a language's grammar, picking apart the way something is said tends not to advance the discussion as well as repling to content would, however dubiously it may be expressed.
> Passive voice also elides these serious issues by pinning results on nebulous activity.
No, no, no.
Firethief has already largely covered this, but: "Subject" and "passive voice" are grammatical terms. They have to do with the syntax of a sentence. Not with who performed an action, or whether that agency was clearly expressed in the sentence. There is nothing necessarily agency-hiding about the passive voice; conversely, one can hide agency quite well without using it.
Basically, go read some Language Log, they talk about this all the time. Hell, they've got a whole category for people complaining about the passive voice while not actually being able to identify when a sentence uses it: http://languagelog.ldc.upenn.edu/nll/?cat=54
(Edit: One particular post on the subject I should point out, I think -- http://languagelog.ldc.upenn.edu/nll/?p=1227 )
Or here's a whole paper by Geoff Pullum on the subject, with more examples than you can shake a stick at in section 3: http://www.lel.ed.ac.uk/~gpullum/passive_loathing.pdf
Don't get me wrong, I like Tor, but I also understand the pragmatism in law enforcement being a bit interested in people trying that hard to hide what they are doing online.
This is a curious construction, one that I can't pin down to any kind of secondary-language issues. "Using Tor" is not the subject of that sentence, "who's looking" is. So, some people see Tor as suspicious. Who are those people, and why is it a problem? Law enforcement...anybody else?
What does it mean for Tor traffic to be demeaned by law enforcement (or $chosen_group) as by-default suspicious, and is this a good use of their time and resources? Is it a good way to solve crimes? History tells us that law enforcement, and by extension the government, will use bigotry to effect prosecutorial goals at least as readily as they will shoe-leather investigation. Defining Tor as suspicious-with-exceptions operates in the same sphere as asset forfeitture: prove you ain't.
Point being, I think it's important to be clear what is happening with Tor as a character in the wider world of politics and policy, and "using Tor" is something that I don't think needs to be justified. Passive voice also elides these serious issues by pinning results on nebulous activity.