There's a right way and a wrong way to use violence.
…I refer, of course, to the word in the English language. "Violence" has joined a long list of words hijacked for purposes of argumentative rhetoric, selectively misapplied in order to take advantage of their negative (or positive) emotional associations, removing us one step further from constructive debate. Thus, for instance, meat is "murder" (as that Smiths song goes), maternity leave is "socialism", Israel is a "colonialist power", and taxation is "violent".
This last example, especially popular among libertarians, refers to the fact that taxpayers, well, taxpay quite reluctantly (to say the least), without having free choice in the matter. libertarians' negative view of this state of affairs comes as part of a larger worldview that is especially abhorrent of any kind of involuntary action (in the 2nd dictionary sense). While perfectly legitimate as such, some proponents of this viewpoint nevertheless distort(2) language when insisting to misconstrue taxation as "violent".
Consider the following nuances of definition:
Force¹ – v. [with obj.] – ⑵ make (someone) do something against their will.
Coerce – v. [with obj.] – persuade (an unwilling person) to do something by using force or threats.
Violent – adj. – ⑴ using or involving physical force intended to hurt, damage, or kill someone or something.
– from the New Oxford American Dictionary, 3rd ed., also at oxforddictionaries.com
Presumably even the most freedom-loving individual can find in the first two words a negative enough association to attach to taxation – while still presenting a reasonably true description. Most taxpayers are indeed forced to pay, one might argue that they are coerced. but where is the direct, physical, club-on-head action in taxation?
"Ah," replies the well-versed libertarian, "but taxation most certainly is violence. If you avoid paying taxes long enough, men with guns (MWG) will come to your house and exhibit all sorts of behavior involving physical force intended to hurt, damage, or kill someone or something!"
I'll get to the main problem with this in a moment. On a side note, I'd argue that the above generalization is a bit of a stretch: how many tax evaders (and minor law offenders) get away with a slap on the wrist, or less, every day? Also, libertarians often downplay the fact that they condone this kind of ultimate threat of "violence" for purposes they approve of, like law enforcement (however minimal), military defense, and defense of private property rights; I have yet to hear a libertarian bemoan how, in a libertarian society, all of these would be backed by their version of "violence".
But all of this is debatable, and secondary. The main problem is that even if the MWG scenario were true, using the word "violence" to describe taxation is equating a potential outcome, when exacerbated to an extreme¹ – "if you refuse to pay taxes…" – with the state being discussed (taxation). (This is a line of argument I've mentioned before.) Unless that's already in the definition of the word, it is an error to use it as such. X isn't Y just because it might come to be Y. By the same logic, any assembly of people is a riotous coup (a pet argument of libertarians), not eating is the same as starvation, and annoying someone is the same as being killed by them in a fit of rage.
Thus, if one insists on invoking violence towards taxation, the closest one can get is to say that taxation is backed by the threat of violence (just as any law in a libertarian reality would). And there's already a perfectly good word for that – coercion. Even here, I would argue it remains to be demonstrated categorically that in the event of serial tax evasion, the taxation Men With Guns – who presumably would come banging on the evader's door – would in fact intend to hurt, damage, or kill someone and not, say, carry out economic sanctions (like foreclosure), or an arrest – without intent to hurt anyone. (That police violence occurs doesn't negate this.) But again, that's debatable, and one needn't agree with it to accept my central argument. Taxation "is" no more violent than private property "is" violent.
None of this is to say there's no room to criticize, analyze, or reassess taxation. But the discussion would be much more effective without the red herring of misleading terminology.
A word on the definitions: I'm big on the New Oxford American Dictionary, but lest I appear to have favored a particular definition for its convenience, here are a few more dictionary entries for "violence". You'll notice how all of them refer to the actual act of physical force – not a potential threat of using it, however inescapably, somewhere down the road – and state a physically destructive intent, rather than purposes such as tax collection.