John Locke takes for granted the necessity of taxes, but stipulates three conditions for taxes and other government appropriations of property to be legitimate. 

    The taxes cannot be so high that some individuals would be better off in the state of nature than as taxpayers within the nation. 

    The taxes must be approved by some kind of majority vote of the populace representatives of the populace who still have the interests of the populace at heart. 

    The taxes must be for the good of the nation as a whole—or at least include among their beneficiaries many who are not themselves politically powerful. 

These views are laid out in John Locke’s 2d Treatise on Government: Of Civil Government, Chapter XI (“Of the Extent of the Legislative Power”), Sections 138-140.

The first point—that taxes cannot be so high that some individuals would be better off in the state of nature instead, I infer from the beginning of Section 138:

 §. 138. Thirdly, The supreme power cannot take from any man any part of his property without his own consent: for the preservation of property being the end of government, and that for which men enter into society, it necessarily supposes and requires, that the people should have property, without which they must be supposed to lose that, by entering into society, which was the end for which they entered into it: too gross an absurdity for any man to own. 

The remainder of Section 138 sets forth the need for representatives to approve taxes who still have the populace’s interests at heart:

Men therefore in society having property, they have such a right to the goods, which by the law of the community are theirs, that nobody hath a right to take their substance or any part of it from them, without their own consent: without this they have no property at all; for I have truly no property in that, which another can by right take from me, when he pleases, against my consent. Hence it is a mistake to think, that the supreme or legislative power of any commonwealth can do what it will, and dispose of the estates of the subject arbitrarily, or take any part of them at pleasure. This is not much to be feared in governments where the legislative consists, wholly or in part, in assemblies which are variable, whose members, upon the dissolution of the assembly, are subjects under the common laws of their country, equally with the rest. But in governments, where the legislative is in one lasting assembly always in being, or in one man, as in absolute monarchies, there is danger still, that they will think themselves to have a distinct interest from the rest of the community; and so will be apt to increase their own riches and power, by taking what they think fit from the people: for a man’s property is not at all secure, though there be good and equitable laws to set the bounds of it between him and his fellow subjects, if he who commands those subjects have power to take from any private man, what part he pleases of his property, and use and dispose of it as he thinks good. 

The beginning of Section 139 then speaks of “consent”:

§. 139. But government, into whatsoever hands it is put, being, as I have before shewed, intrusted with this condition, and for this end, that men might have and secure their properties; the prince, or senate, however it may have power to make laws, for the regulating of property between the subjects one amongst another, yet can never have a power to take to themselves the whole, or any part of the subjects’ property, without their own consent: for this would be in effect to leave them no property at all. 

Consent is then defined in Section 140 as majority approval:

§. 140. It is true, governments cannot be supported without great charge, and it is fit every one who enjoys his share of the protection should pay out of his estate his proportion for the maintenance of it. But still it must be with his own consent, i. e. the consent of the majority, giving it either by themselves, or their representatives chosen by them: for if any one shall claim a power to lay and levy taxes on the people, by his own authority, and without such consent of the people, he thereby invades the fundamental law of property, and subverts the end of government: for what property have I in that, which another may by right take, when he pleases, to himself?

For current debates, John Locke’s most important stipulation is about the legitimate purposes of taxation. In  the latter part of Section 139, he is not explicit about exactly what purposes are appropriate, but has a very revealing parable: a general can order a soldier to almost certain for a public purpose—the preservation of the nation from destruction by its enemies in war—but cannot legitimately steal a penny from the soldier for the general’s personal enrichment: 

§. 139. … And to let us see, that even absolute power, where it is necessary, is not arbitrary by being absolute, but is still limited by that reason, and confined to those ends, which required it in some cases to be absolute, we need look no farther than the common practice of martial discipline: for the preservation of the army, and in it of the whole commonwealth, requires an absolute obedience to the command of every superior officer, and it is justly death to disobey or dispute the most dangerous or unreasonable of them; but yet we see, that neither the serjeant, that could command a soldier to march up to the mouth of a cannon, or stand in a breach, where he is almost sure to perish, can command that soldier to give him one penny of his money; nor the general, that can condemn him to death for deserting his post, or for not obeying the most desperate orders, can yet, with all his absolute power of life and death, dispose of one farthing of that soldier’s estate, or seize one jot of his goods; whom yet he can command any thing, and hang for the least disobedience; because such a blind obedience is necessary to that end, for which the commander has his power, viz. the preservation of the rest; but the disposing of his goods has nothing to do with it.

Debates about quantity and procedure for taxes are frequent and obvious in the news. Debates about purpose of taxes are even more frequent, but come in a slightly different guise: they show up as debates about whether particular government expenditures are appropriate or not. In many countries, the battle for what John Locke argues for in these three sections has been won. We are fortunate to have democratic governance of taxes and government spending.  

“Taxation is theft, purely and simply even though it is theft on a grand and colossal scale which no acknowledged criminals could hope to match. It is a compulsory seizure of the property of the State’s inhabitants, or subjects.”

― Murray N. Rothbard